Long-term Pooled Safety Analysis of Palbociclib in Combination With Endocrine Therapy for HR+/HER2- Advanced Breast Cancer

Dose reduction and discontinuation due to the combination of CDK4/6 inhibitors and endocrine drugs: a systematic review and meta-analysis

BACKGROUND

With the widespread use of CDK4/6 inhibitors, the number of discontinuations and reductions due to adverse events is increasing. Therefore, we examined the risk of dose reduction, discontinuation, and occurrence of serious adverse events and death due to adverse events when CDK4/6 inhibitors are combined with endocrine drugs.

METHODS

We searched English-language articles published up to February 10, 2024, using RR values (risk ratio) to indicate the risk of discontinuation, dose reduction, death, and the risk of serious adverse events.

RESULTS

When CDK4/6 inhibitors were used in combination with endocrine drugs, abemaciclib resulted in the highest risk of discontinuation, dose reduction, and serious adverse events. Ribociclib caused the highest risk of death.

CONCLUSION

When using CDK4/6 inhibitors in the clinical setting, a comprehensive evaluation should be performed to avoid dosage reductions and discontinuations and to choose the most appropriate treatment regimen.

Acute Lymphoblastic Leukemia in a Patient With Advanced Breast Cancer Treated With Cyclin-Dependent Kinase 4/6 Inhibitors and Endocrine Therapy

This case shares the case of a post-menopausal woman who develops Philadelphia chromosome-positive B cell acute lymphoblastic leukemia (B-ALL) while receiving treatment for invasive ductal carcinoma (IDC) of the breast. The patient received a cyclin-dependent kinase (CDK) 4/6 inhibitor + aromatase inhibitor (AI) for the IDC; hyperfractionate cyclophosphamide, vincristine sulfate, doxorubicin hydrochloride (Adriamycin), methotrexate, and cytarabine (hyperCVAD), and the steroid hormone dexamethasone were added to treat the B-ALL. HyperCVAD combined with CDK 4/6 inhibitor + AI was very well tolerated. The CDK 4/6 inhibitor and AI were only held once in the treatment course due to adverse effect (AE) intolerance. The patient remains on a CDK 4/6 inhibitor and ponatinib with only low-grade fatigue as an AE. This case underscores the importance of a concurrent approach to managing hematologic and breast malignancies. The combined treatment regimens were effective and well-tolerated. Vigilant follow-up is essential for patients in remission from both malignancies, ensuring effective disease surveillance and treatment management. Integrated care remains pivotal for optimal outcomes.

Potential association of SULT2A1 and ABCG2 variant alleles with increased risk for palbociclib toxicity

Aim: This study evaluated associations between CYP3A4*22 and variants in other pharmacogenes (CYP3A5, SULT2A1, ABCB1, ABCG2, ERCC1) and the risk for palbociclib-associated toxicities.Materials & methods: Two hundred cancer patients who received standard-of-care palbociclib were genotyped and associations with toxicity were evaluated retrospectively.Results: No significant associations were found for CYP3A4*22, CYP3A5*3, ABCB1_rs1045642, ABCG2_rs2231142, ERCC1_rs3212986 and ERCC1_rs11615. Homozygous variant carriers of SULT2A1_rs182420 had higher incidence of dose modifications due to palbociclib toxicity (odds ratio [OR]: 4.334, 95% CI: 1.057-17.767, p = 0.042). ABCG2_rs2231137 variant carriers had borderline higher incidence of grade 3-4 neutropenia (OR: 4.14, 95% CI: 0.99-17.37, p = 0.052).Conclusion: Once validated, SULT2A1 and ABCG2 variants may be useful to individualize palbociclib dosing to minimize toxicities and improve treatment outcomes.

Randomized Phase III Study of Amcenestrant Plus Palbociclib Versus Letrozole Plus Palbociclib in Estrogen Receptor-Positive, Human Epidermal Growth Factor Receptor 2-Negative Advanced Breast Cancer: Primary Results From AMEERA-5

PURPOSE

AMEERA-5 investigated amcenestrant (oral selective estrogen receptor [ER] degrader) plus palbociclib versus letrozole plus palbociclib as first-line treatment for ER-positive/human epidermal growth factor receptor 2-negative (ER+/HER2-) advanced/metastatic breast cancer (aBC).

MATERIALS AND METHODS

In AMEERA-5 (ClinicalTrials.gov identifier: NCT04478266), a double-blind, double-dummy, international phase III trial, adult pre-/post-menopausal women and men without previous systemic therapy for ER+/HER2- aBC were randomly assigned 1:1 to amcenestrant 200 mg once daily + standard palbociclib dosage (125 mg once daily, 21 days on/7 days off) or letrozole 2.5 mg once daily + standard palbociclib dosage, stratified by de novo metastatic disease, postmenopausal women, and visceral metastasis. The primary end point was progression-free survival (PFS), compared using a stratified log-rank test with one-sided type I error rate of 2.5%. Secondary end points included overall survival (key secondary), pharmacokinetics, and safety.

RESULTS

Between October 14, 2020, and December 2, 2021, 1,068 patients were randomly assigned to amcenestrant + palbociclib (N = 534) or letrozole + palbociclib (N = 534). At the interim analysis (median follow-up 8.4 months), the stratified hazard ratio for PFS was 1.209 (95% CI, 0.939 to 1.557; one-sided P value = .9304); therefore, the study was stopped for futility. The 6-month PFS rate was 82.7% (95% CI, 79.0 to 85.8) with amcenestrant + palbociclib versus 86.9% (95% CI, 83.5 to 89.6) with letrozole + palbociclib. In the amcenestrant + palbociclib versus letrozole + palbociclib groups, treatment-emergent adverse events (any grade) occurred in 85.6% versus 85.4% of patients and grade ≥3 events in 46.3% versus 60.8%, respectively.

CONCLUSION

The AMEERA-5 study was discontinued on the basis of the recommendation of the data monitoring committee at the interim futility analysis. No new safety signals were identified.

Initial ribociclib plus endocrine therapy for HR+/HER2- advanced breast cancer in pre- and postmenopausal Chinese women: Primary results from a phase 2 randomized study

Background

The MONALEESA‐7 and ‐2 phase 3 randomized trials demonstrated a statistically significant progression‐free survival (PFS) and overall survival (OS) benefit with initial ribociclib + endocrine therapy (ET) versus placebo + ET in pre‐ and postmenopausal patients with hormone receptor–positive (HR+)/human epidermal growth factor receptor 2–negative (HER2−) advanced breast cancer (ABC), respectively. Similar trends were observed in Asian subgroup analyses. This phase 2 bridging study of initial ET + ribociclib enrolled pre‐ and postmenopausal patients with HR+/HER2– ABC from China and was conducted to demonstrate consistency of PFS results in a Chinese population relative to the global MONALEESA‐7 and ‐2 studies.

Methods

Patients were randomized (1:1) to ET (nonsteroidal aromatase inhibitor + goserelin for premenopausal patients; letrozole for postmenopausal patients) + either ribociclib or placebo. The primary endpoint was investigator‐assessed PFS.

Results

As of April 25, 2022, the median follow‐up was 34.7 months in both cohorts. In the premenopausal cohort, median PFS was 27.6 months in the ribociclib arm (n = 79) versus 14.7 months in the placebo arm (n = 77) (hazard ratio 0.67 [95% CI: 0.45, 1.01]). In the postmenopausal cohort, median PFS was not reached in the ribociclib arm versus 18.5 months in the placebo arm (n = 77 in each arm) (hazard ratio 0.40 [95% CI: 0.26, 0.62]). Data also suggested improvements in secondary efficacy endpoints, although OS data were not mature. The safety profile in this population was consistent with that in global studies.

Conclusions

These data demonstrate a favorable benefit–risk profile for ribociclib + ET in Chinese patients.

Oral SERDs alone or in combination with CDK 4/6 inhibitors in breast cancer: Current perspectives and clinical trials

Over the past few decades, first-line therapy for treating advanced and metastatic HR+/HER2-breast cancer has transformed due to the introduction of adjuvant endocrine therapy with cyclin-dependent kinase 4/6 inhibitors (CDK 4/6i). However, there is an unmet need for novel classes of endocrine therapy with superior efficacy to improve treatment outcomes and overcome CDK4/6i resistance. New generation selective estrogen receptor degraders (SERDs), orally administered and with higher bioavailability, could potentially be the novel compounds to meet this emerging need. In this paper, we review accredited clinical studies on the combining effects of CDK4/6 inhibitors and oral SERDs, report efficacy of treatment data when available, and provide a framework for future research focusing on these promising agents.

The efficacy of palbociclib and ribociclib in the first-line treatment of metastatic hormone receptor-positive, human epidermal growth factor receptor 2-negative breast cancer in male patients: a Turkish oncology group (TOG) study

INTRODUCTION

Male breast cancer, comprising approximately 1% of all breast cancer cases, often leads to the exclusion of male patients as a criterion in clinical trials. While the efficacy of Cyclin-dependent kinases 4 and 6 (CDK 4/6) inhibitors has been established in metastatic hormone receptor-positive (HR +) and human epidermal growth factor receptor 2-negative (HER2 -) breast cancer in women, limited data exist on their effectiveness in male patients. We aimed to evaluate the efficacy and safety of palbociclib or ribociclib in male patients with breast cancer.

METHODS

This study is a multicenter, retrospective study. We included male patients with HR + and HER2-metastatic breast cancer who received palbociclib or ribociclib as first-line treatment. Our primary endpoints were progression-free survival (PFS), overall response rates (ORR), and drug-related adverse effects.

RESULTS

A total of 46 male patients from 27 institutions were enrolled. The median age at initiation of CDK 4/6 inhibitors was 63.64 ± 13.69 years, with a median follow-up of 21.33 (95% CI 14.92-27.74) months. The ORR were 84% for palbociclib and 76.2% for ribociclib. The mPFS for the entire cohort was 28.06 months (95% CI 18.70-37.42). No significant difference in PFS was observed between palbociclib and ribociclib (mPFS: 24.46 months (95% CI 11.51-37.42) vs 28.33 months (95% CI 14.77-41.88), respectively, p = 0.211). No new adverse events were reported.

DISCUSSION

This study demonstrates that palbociclib and ribociclib are effective and safe options for first-line treatment in male patients with HR + /HER2 - metastatic breast cancer. However, further prospective studies are warranted to establish their efficacy in this population.

CDK4/6 inhibitors in the treatment of metastatic breast cancer: Focus on toxicity and safety

The development of oral cyclin-dependent kinases 4 and 6 (CDK4/6) inhibitors, including palbociclib, ribociclib, and abemaciclib, has revolutionized the treatment landscape for patients with hormone-receptor-positive (HR+) and human epidermal growth factor receptor 2 (HER2)-negative metastatic breast cancer (BC). When combined with an aromatase inhibitor or fulvestrant, these agents have been approved as first-line therapy in the metastatic setting. Abemaciclib has also gained FDA approval for patients with HR-positive, HER2-negative, node-positive, early BC at high risk of recurrence. Moreover, ribociclib has recently improved disease-free survival in patients with stage II or III HR+/HER2-negative early BC. CDK4/6 inhibitors have favorable safety profiles. However, the available agents have different toxicity profiles that must be clearly discussed with the patients for optimal clinical decisions. This manuscript aims to review CDK4/6 inhibitor-related treatment-associated adverse events, identify risk factors for intolerable adverse events, and assess their safety in special patient populations such as the elderly and those with renal insufficiency. Enhanced knowledge and understanding of CDK4/6 inhibitor-related toxicities can improve treatment strategies and ultimately enhance patient care.

Neoadjuvant nivolumab + palbociclib + anastrozole for oestrogen receptor-positive/human epidermal growth factor receptor 2-negative primary breast cancer: Results from CheckMate 7A8

BACKGROUND

Preclinical data suggest synergistic activity with the combination of programmed death-1 and cyclin-dependent kinase 4/6 blockade in oestrogen receptor-positive/human epidermal growth factor 2-negative (ER+/HER2-) breast cancer. The noncomparative phase 1b/2 CheckMate 7A8 study (NCT04075604) evaluated neoadjuvant treatment with nivolumab, palbociclib, and anastrozole in patients with ER+/HER2- breast cancer. Here, we report outcomes from the safety run-in phase.

METHODS

Patients with histologically confirmed, untreated ER+/HER2- breast cancer, primary tumour ≥2 cm, ECOG performance status ≤1, and eligible for post-treatment surgery received nivolumab 480 mg intravenously every 4 weeks, palbociclib 125 mg or 100 mg orally once daily for 3 weeks per cycle, and anastrozole 1 mg orally once daily for five 4-week cycles, or until disease progression. The primary endpoint was the proportion of patients with dose-limiting toxicities (DLTs) within 4 weeks of treatment initiation.

RESULTS

At safety data review, 21 patients were treated (palbociclib 125-mg group: n = 9; palbociclib 100-mg group: n = 12). DLTs were reported in 2 (22.2%) and 0 patients in the palbociclib 125-mg and 100-mg groups, respectively. Across both groups, 9 patients discontinued treatment due to toxicity (grade 3/4 hepatic adverse events [n = 6], grade 3 febrile neutropaenia [n = 1], grade 1 pneumonitis [n = 1], and grade 3 rash and grade 2 immune-mediated pneumonitis [n = 1]). Consequently, the study was closed early.

CONCLUSIONS

Neoadjuvant treatment with nivolumab, palbociclib, and anastrozole showed a high incidence of grade 3/4 hepatotoxicity and treatment discontinuation, indicating that this combination should not be further pursued for treatment of primary ER+/HER2- breast cancer.

A multicentre study with real-world data of the use of palbociclib in the treatment of breast cancer: Treatment duration correlates with dose reductions

OBJECTIVE

Palbociclib, a highly selective reversible CDK4-6 kinase inhibitor, is indicated in combination with an aromatase inhibitor or in combination with fulvestrant in women who had received prior endocrine treatment. Studies have demonstrated the efficacy of palbociclib in combination with fulvestrant in increasing progression-free survival in patients who relapsed or progressed on previous endocrine therapy, or in combination with aromatase inhibitor in patients who had not received previous treatments. We analysed the prescribing patterns of palbociclib in real practice correlating it with the evidence of treatment-related toxicity management and to time-to-treatment discontinuation and treatment adherence.

METHODS

For the observational, retrospective study, data were collected from five Italian hospital centres that prescribed palbociclib between April 2017 and April 2020. Each centre provided data derived from an administrative database of adult patients treated with palbociclib for the two therapeutic indications.Treatment adherence was calculated using the proportion of days covered method while time-to-treatment discontinuation was defined as the difference between the first and last date treatment was administered plus the days ideally covered by the last date treatment was given.

RESULTS

There were 375 patients enrolled during the study period, of whom 159 were treated with palbociclib and aromatase inhibitor and 216 were treated with palbociclib and fulvestrant. The time-to-treatment discontinuation was 8.9 months in the case of P + f (95% CI: 7.1-12.7) and 13.7 months in the case of P + ia (95% CI: 8.9-17.5). In both cohorts, treatments that received at least one dose reduction had a statistically higher time-to-treatment discontinuation than those without dose reduction (17.7 months vs. 9.2 and 16.6 vs. 7.4).The mean adherence in our study was 0.9 and remained high in treatments with one dose reduction (0.83) and this with two dose reductions (0.87).

CONCLUSION

Based on these findings, it appears that the management of toxicities through reducing doses, as required by the Summary of Product Characteristics, results in a better outcome in terms of therapy duration, and therefore time to failure due to progression or toxicity.

Hematological Events Potentially Associated with CDK4/6 Inhibitors: An Analysis from the European Spontaneous Adverse Event Reporting System

Cyclin-dependent kinases 4 and 6 (CDK4/6) inhibitors are a recent targeted therapy approved for patients with hormone receptor-positive (HR+), human epidermal growth factor receptor 2 negative (HER2-) advanced breast cancer. Abemaciclib, palbociclib and ribociclib demonstrated great efficacy and safety during clinical studies. However, differences in their adverse-event profiles have been observed. This work aims to describe the suspected adverse drug reactions (ADRs), such as leukopenia and thrombocytopenia, reported for each CDK4/6 inhibitor in the EudraVigilance (EV) database. Data on individual case safety reports (ICSRs) were obtained by accessing the European spontaneous reporting system via the EV website. Information on concomitant drug therapy, including fulvestrant, letrozole, anastrozole and exemestane, was also analyzed. A total of 1611 ICSRs were collected from the EV database. Most reports of palbociclib and ribociclib were classified as serious cases for both suspected leukopenia and thrombocytopenia ADRs. However, most patients had their leukopenia and thrombocytopenia recovered/resolved. On the contrary, reports of abemaciclib were mostly characterized as non-serious cases. Abemaciclib and palbociclib were often combined with fulvestrant, while ribociclib was generally associated with letrozole. Pharmacovigilance studies are crucial for the early identification of potential ADRs and to better differentiate the toxicity profile of the different CDK4/6 inhibitors, particularly in a real-world setting.

Cyclin-dependent kinase 4/6 inhibitor treatment use in women treated for advanced breast cancer: Integrating ASCO/NCODA patient-centered standards in a community pharmacy

BACKGROUND

Outpatients treated with oral anti-cancer drugs, including selective cyclin-dependent kinase 4/6 inhibitors (CDK4/6i), may benefit from a pharmacy practice setting adapted to support proper oral anti-cancer drug monitoring. This real-world study aimed to characterize patient-centered pharmacy practice aligned with American Society of Clinical Oncology (ASCO)/National Community Oncology Dispensing Association (NCODA) standards and to describe its impact on CDK4/6i treatment use.

METHODS

This retrospective study included women with confirmed hormone receptor-positive/human epidermal growth factor 2 negative locally advanced or metastatic breast cancer treated with either palbociclib, abemaciclib or ribociclib combined with letrozole or fulvestrant. Pharmacists collected patient characteristics, clinical activities, and treatment patterns using data from the pharmacy chart. CDK4/6i treatment adherence rates were estimated based on medication claims data. Time-to-treatment discontinuation, a proxy for time-to-event, was assessed using the Kaplan-Meier estimate.

RESULTS

Of the 195 patients assessed for eligibility, 65 were included in this study. The median observation duration was 13.6 months. An average of seven pharmaceutical care activities (range 2.8-21.7) per patient was documented for each treatment cycle. The mean proportion of days covered was 89.6%. The median time-to-treatment discontinuation was estimated at 44.2 months in patients treated with CDK4/6i + letrozole and 17.0 months in patients treated with CDK4/6i + fulvestrant. The average relative dose intensity was 85%, and the benefits of treatment were maintained regardless of the relative dose intensity levels.

CONCLUSION

A structured patient-centered pharmacy practice model integrating the ASCO/NCODA patient-centered standards and ongoing communication with patients and healthcare providers ensure timely refills, close monitoring, and allows patients to achieve high adherence and persistence rates comparable to those reported in clinical trials.

Firing of Replication Origins Is Disturbed by a CDK4/6 Inhibitor in a pRb-Independent Manner

Over the last decade, CDK4/6 inhibitors (palbociclib, ribociclib and abemaciclib) have emerged as promising anticancer drugs. Numerous studies have demonstrated that CDK4/6 inhibitors efficiently block the pRb-E2F pathway and induce cell cycle arrest in pRb-proficient cells. Based on these studies, the inhibitors have been approved by the FDA for treatment of advanced hormonal receptor (HR) positive breast cancers in combination with hormonal therapy. However, some evidence has recently shown unexpected effects of the inhibitors, underlining a need to characterize the effects of CDK4/6 inhibitors beyond pRb. Our study demonstrates how palbociclib impairs origin firing in the DNA replication process in pRb-deficient cell lines. Strikingly, despite the absence of pRb, cells treated with palbociclib synthesize less DNA while showing no cell cycle arrest. Furthermore, this CDK4/6 inhibitor treatment disturbs the temporal program of DNA replication and reduces the density of replication forks. Cells treated with palbociclib show a defect in the loading of the Pre-initiation complex (Pre-IC) proteins on chromatin, indicating a reduced initiation of DNA replication. Our findings highlight hidden effects of palbociclib on the dynamics of DNA replication and of its cytotoxic consequences on cell viability in the absence of pRb. This study provides a potential therapeutic application of palbociclib in combination with other drugs to target genomic instability in pRB-deficient cancers.

Risk Factors for Palbociclib-Induced Early Developing Neutropenia in Patients with Hormone Receptor-Positive Metastatic Breast Cancer

PURPOSE

This study aimed to determine the risk factors for palbociclib-induced grade 4 or grade 3 neutropenia (NP) requiring dose reduction or delayed treatment in patients with HR+/HER2-metastatic breast cancer in the first 3 cycles (early grade 3/4 NP) and whether the early developing grade 3/4 NP affects progression-free survival.

METHODS

A retrospective study using electronic medical records was conducted on patients who received palbociclib for metastatic breast cancer between January 2018 and August 2022. The early grade 3/4 NP risk factors were evaluated with univariate and multivariable logistic regression analyses. In addition, the Kaplan-Meier method was used to estimate the median progression-free survival (PFS) to analyze the effect of early grade 3/4 NP on treatment.

RESULTS

Out of the 264 patients included in this study, 173 (65.6%) experienced early grade 3/4 NP. A total of four models were applied for multivariable analysis to identify early grade 3/4 NP-developing factors. Low baseline ANC, WBC, PLT, and BSA were significant risk factors for early grade 3/4 NP; baseline ANC < 3700/mm³, WBC < 6.30 × 10⁹/mm³, PLT < 230 × 10⁹/mm³, and BSA < 1.58 m² increased the risk by approximately 4.0-fold, 3.7-4.0-fold, 2.1-fold, and 2.0-fold, respectively. Early grade 3/4 NP did not affect PFS (p = 0.710), although patients with early grade 3/4 NP had more frequent dose reductions or treatment delays.

CONCLUSIONS

Based on the results, low baseline ANC, WBC, PLT, and BSA were associated with early grade 3/4 NP. Patients with risk factors require careful monitoring, and this study is expected to help predict NP, which may appear in early treatment.

Abemaciclib, Palbociclib, and Ribociclib in Real-World Data: A Direct Comparison of First-Line Treatment for Endocrine-Receptor-Positive Metastatic Breast Cancer

By the end of 2020, there were more than 8 million women alive who had received a breast cancer diagnosis in the previous 5 years, making it the most prevalent neoplasia in the world. About 70% of breast-cancer cases present positivity for estrogen and/or progesterone receptors and a lack of HER-2 overexpression. Endocrine therapy has traditionally been the standard of care for ER-positive and HER-2-negative metastatic breast cancer. In the last 8 years, the advent of CDK4/6 inhibitors has shown that adding them to endocrine therapy doubles PFS. As a result, this combination has become the gold standard in this setting. Three CDK4/6 inhibitors have been approved by the EMA and the FDA: abemaciclib, palbociclib, and ribociclib. They all have the same indications, and it is at each physician's discretion to choose one or the other. The aim of our study was to perform a comparative efficacy analysis of the three CDK4/6i using real-world data. We selected patients diagnosed with endocrine-receptor-positive and HER2-negative breast cancer who were treated with all three CDK4/6i as first-line therapy at a reference center. After 42 months of retrospective follow up, abemaciclib was associated with a significant benefit in terms of progression-free survival in endocrine-resistant patients and in the population without visceral involvement. In our real-world cohort, we found no other statistically significant differences among the three CDK4/6 inhibitors.

The likelihood of being helped or harmed as a patient-centred tool to assess cyclin dependent kinase 4/6 inhibitors clinical impact and safety in metastatic breast cancer: a systematic review and sensitivity-analysis

Background

In hormone-receptor positive/HER2-negative metastatic breast cancer (mBC) no randomized comparisons are available between CDK4/6 inhibitors. We undertook this systematic review and meta-analysis to assess the reliability of the likelihood of being helped or harmed (LHH).

Methods

PubMed, CENTRAL, Embase and oncological meetings websites were searched to September 13th, 2022. We included phase III randomized controlled trials (RCTs) investigating palbociclib, ribociclib and abemaciclib in addition to endocrine therapy (ET) compared to placebo in hormone-receptor positive/HER2-negative advanced or mBC. Outcomes were progression-free survival (PFS), overall survival (OS), adverse events (AEs), dose reductions and discontinuations. Hazard ratios (HRs) and risk differences were computed with a random effect model to estimate the number needed to treat/harm (NNT/NNH). LHH was computed as (1/NNT)/(1/NNH). PROSPERO registration number: CRD42022362417.

Findings

2204 records were screened and seven RCTs (4415 patients) were included. A significant PFS benefit was observed in patients treated with a CDK4/6 inhibitor compared to placebo (HR 0.549; 0.508-0.594, I 2  = 0). Palbociclib, ribociclib and abemaciclib had similar NNTs (4.4, 5.0 and 4.4). Palbociclib and ribociclib showed lower LHHs for grade 3-4 neutropenia (0.33 and 0.35) and febrile neutropenia ([FN], 14.27 and 15.52), while abemaciclib the lowest LHH for any grade diarrhea (0.42). Abemaciclib had a lower LHH for grade 3-4 fatigue (9.92) and the highest LHH for all grade 3-4 AEs (0.62), while ribociclib the lowest LHH (1.75) for grade 3-4 hepatotoxicity. Palbociclib had the highest LHH for dose reductions and discontinuations (0.65 and 6.17). Considering OS, an overall benefit was observed (HR 0.788, 0.727-0.856, I 2  = 0%); ribociclib and abemaciclib had lower NNTs (9.7 and 10.0). Ribociclib showed the highest LHH for diarrhea (1.29), fatigue (7.37), dose reductions (0.28) and discontinuations (2.40), while abemaciclib the highest LHHs for neutropenia (0.40), FN (12.53) and hepatotoxicity (2.23).

Interpretation

Palbociclib and ribociclib showed lower LHHs for haematological toxicities and abemaciclib for diarrhea. Palbociclib confirmed to be a manageable drug. The LHH appears to be a reliable synthesis tool for balancing risks and benefits of experimental drugs when head-to-head comparisons are missing.

Funding

None.

Clinical features of CDK4/6 inhibitor-related interstitial lung disease in patients with breast cancer: a case series study

BACKGROUND

Cyclin-dependent kinase 4/6 (CDK4/6) inhibitors are the standard treatment for advanced hormone receptor-positive breast cancer. Although interstitial lung disease is a rare (1-3.3%) but serious adverse event associated with CDK4/6 inhibitors, the incidence of interstitial lung disease in Japanese patients in the real world and the risk factors of interstitial lung disease are not clear.

METHODS

We retrospectively investigated the incidence of interstitial lung disease in 224 patients with advanced breast cancer who received CDK4/6 inhibitors at our hospital between 31 January 2017 and 31 January 2021. The correlation of age (>50 vs ≤50 years), presence or absence of previous history of interstitial lung disease, lung metastasis, smoking history and chest radiation with the development of interstitial lung disease was evaluated.

RESULTS

In total, 177 cases received palbociclib, 39 cases received abemaciclib and 8 cases received both palbociclib and abemaciclib, constituting a palbociclib group (n = 185) and an abemaciclib group (n = 47). At a median observation period of 607 days, 8.0% (18/224) cases (13 definite and 5 probable cases) had interstitial lung disease; 6.5% (12/185) of palbociclib-treated and 13% (6/47) of abemaciclib-treated cases. The median time to interstitial lung disease onset was 178 (range, 14-750) days. There was no significant correlation between the background factors studied and the development of interstitial lung disease.

CONCLUSION

The frequency of CDK4/6 inhibitor-induced interstitial lung disease was higher than that reported in clinical trials. We did not identify any risk factors for the development of interstitial lung disease in this study, and thus, larger studies that include patient predisposition are required.

Patient characteristics, treatment patterns, and outcomes of hormone receptor-positive, human epidermal growth factor receptor 2-negative advanced breast cancer patients prescribed cyclin-dependent kinase 4 and 6 inhibitors: large-scale data analysis using a Japanese claims database

PURPOSE

The aim was to understand real-world cyclin-dependent kinase (CDK) 4 and 6 inhibitor use in Japan.

METHODS

This retrospective observational study used a Japanese administrative claims database and included patients with presumptive hormone receptor-positive, human epidermal growth factor receptor 2-negative advanced breast cancer (ABC) prescribed CDK4 and 6 inhibitor therapy between December 2017 and March 2021. Patient characteristics, treatment patterns, and selected clinical and safety outcomes were descriptively summarized. Time to discontinuation (TTD) and chemotherapy-free survival (CFS) were examined using Kaplan-Meier estimates.

RESULTS

The study cohort (N = 6442) was predominantly female (99.4%; median [range] age 64 [26-99] years) with records of metastases (79.6%) within 1 year prior to initiating CDK4 and 6 inhibitor therapy. In total, 4463 (69.3%) and 1979 (30.7%) were prescribed palbociclib and abemaciclib, respectively, as their first CDK4 and 6 inhibitor, most commonly in combination with fulvestrant (n = 3801; 59.0%). Overall, 3756 patients initiated a subsequent anticancer treatment, of whom 748 (19.9%) initiated a different CDK4 and 6 inhibitor in combination with the same or different endocrine therapy. Median TTD (95% confidence interval) was 9.7 (9.3, 10.1) months for the first CDK4 and 6 inhibitor therapy. Median CFS was 26.1 (24.6, 27.8) months. Incidence of clinically relevant diarrhea was higher after abemaciclib initiation (9.8%) than after palbociclib initiation (1.5%). More patients experienced dose reduction with palbociclib (69.3%) than with abemaciclib (53.0%).

CONCLUSION

The data provide insights into current clinical practices for CDK4 and 6 inhibitor use in Japan that could help establish future treatment strategies for ABC.

Palbociclib plus letrozole versus placebo plus letrozole in Asian postmenopausal women with oestrogen receptor-positive/human epidermal growth factor receptor 2-negative advanced breast cancer: Primary results from PALOMA-4

BACKGROUND

The cyclin-dependent kinase 4/6 inhibitor palbociclib has demonstrated efficacy and a manageable safety profile in combination with endocrine therapy in women with oestrogen receptor-positive (ER+)/human epidermal growth factor receptor 2-negative (HER2-) advanced breast cancer (ABC) in international phase 3 trials. The phase 3 PALOMA-4 trial evaluated the efficacy and safety of palbociclib plus letrozole versus placebo plus letrozole in Asian women with ER+/HER2- ABC.

METHODS

Postmenopausal women (n = 340) with no prior systemic treatment for advanced disease were randomised 1:1 to palbociclib (125 mg/d orally; 3 weeks on, 1 week off) plus letrozole (2.5 mg/d orally; continuously) or placebo plus letrozole. The primary end-point was investigator-assessed progression-free survival (PFS). Secondary end-points included tumour response and safety.

RESULTS

Median (95% CI) PFS was 21.5 (16.6-24.9) months with palbociclib plus letrozole and 13.9 (13.7-16.6) months with placebo plus letrozole (hazard ratio, 0.68 [95% CI, 0.53-0.87]; P = 0.0012). Consistent with the established safety profile, the most common adverse events (AEs) with palbociclib plus letrozole were neutropenia, leukopenia, thrombocytopaenia, and anaemia. Grade 3/4 neutropenia was reported in 84.5% of patients in the palbociclib arm versus 1.2% in the placebo arm. One serious AE of febrile neutropenia in the palbociclib group was reported.

CONCLUSIONS

Findings from PALOMA-4 support the efficacy and safety of first-line palbociclib plus letrozole in postmenopausal Asian women with ER+/HER2- ABC. No new safety concerns of palbociclib plus letrozole were identified.

TRIAL REGISTRATION

Clinicaltrials. gov, NCT02297438.

Elevated transaminases and development of cardiomyopathy in a 32-year-old woman with metastatic breast cancer after treatment with ribociclib followed by palbociclib

INTRODUCTION

Cyclin-dependent kinase 4 and 6 inhibitors, ribociclib and palbociclib, are associated with reports of transaminitis and adverse cardiac events.

CASE REPORT

The patient is a previously healthy 32-year-old female diagnosed with estrogen receptor-positive, progesterone receptor-positive, and human epidermal growth factor 2 negative metastatic breast cancer. From July to September 2021, the patient was initiated on ribociclib followed by palbociclib for metastatic breast cancer. She subsequently experienced two episodes of transaminitis and was diagnosed with cardiomyopathy.

MANAGEMENT AND OUTCOME

The patient experienced transaminitis 2 weeks after the initiation of ribociclib resulting in discontinuation. When rechallenged with palbociclib, the patient experienced transaminitis within 1 week of initiation, which resulted in discontinuation. Approximately 1 month after palbociclib discontinuation, the patient was diagnosed with congestive heart failure with a left ventricular ejection fraction of 24%.

DISCUSSION

To our knowledge, there are few case studies investigating cyclin-dependent kinase 4 and 6 inhibitor rechallenge following transaminitis. Prior literature suggests that transaminitis with cyclin-dependent kinase 4 and 6 inhibitors is not a class effect, but this case report suggests otherwise. This report presents a rare case of cardiomyopathy and transaminitis following the administration of cyclin-dependent kinase 4 and 6 inhibitors, ribociclib and palbociclib.

Radiotherapy and CDK inhibitors: Opportunities and risks

CDK4/6 inhibitors are nowadays commonly used in metastatic HR+/HER2- breast cancer. Herein, we report a literature review regarding the benefits and risks of their combination with radiotherapy. Numerous pre-clinical studies have indeed shown a potential synergistic effect of these treatments in combination with radiotherapy in various types of cancers. On the other hand, some retrospective clinical studies have reported increased acute toxicity in case of digestive or pulmonary irradiation; therefore, it is advisable to discontinue CDK4/6 inhibitors before starting irradiation. Several prospective clinical trials are currently ongoing to assess the feasibility of this combination.

Real world incidence and management of adverse events in patients with HR+, HER2- metastatic breast cancer receiving CDK4 and 6 inhibitors in a United States community setting

OBJECTIVE

To examine the real-world incidence and management of select adverse events (AEs) among female patients with hormone receptor positive (HR+), human epidermal growth factor receptor 2-negative (HER2-) metastatic breast cancer (MBC), receiving a cyclin-dependent kinase 4 and 6 (CDK4 and 6) inhibitor (palbociclib, abemaciclib, or ribociclib).

METHODS

This retrospective study analyzed data from the US Oncology Network iKnowMed electronic health record database for 396 patients with an initial MBC diagnosis on/after 1 January 2014 and receipt of first CDK4 and 6 regimen between 1 January 2017 and 31 December 2018. In this descriptive study, the proportion of patients who experienced select AEs and associated dose modifications or discontinuations were reported. The occurrence of select healthcare resource utilization categories was also reported.

RESULTS

Median follow-up time was 451, 262, and 355 days for patients in the palbociclib, abemaciclib, and ribociclib cohorts, respectively. The most common AEs were neutropenia (palbociclib, 44.8%; abemaciclib, 10.6%; ribociclib, 36.3%), diarrhea (palbociclib, 8.0%; abemaciclib, 43.0%; ribociclib, 8.8%), and fatigue (palbociclib, 12.9%; abemaciclib, 17.6%; ribociclib, 16.5%). AEs resulted in a treatment hold among 91 (23.0%), a dose reduction among 86 (21.7%), and permanent discontinuation among 48 (12.1%) patients overall.

CONCLUSIONS

This real-world study provides insight into the occurrence of AEs which varied by CDK4 and 6 inhibitor. Compared to clinical trials, frequencies of AEs were numerically lower but dose reductions due to AEs were numerically higher. It is possible these differences reflect proactive management of AEs on the part of clinicians to help patients remain on therapy.

Pharmacokinetic Variability Drives Palbociclib-Induced Neutropenia in Metastatic Breast Cancer Patients: Drug-Drug Interactions Are the Usual Suspects

Palbociclib is a good candidate for therapeutic drug monitoring (TDM) due to its narrow therapeutic range and frequency of toxicities, particularly high-grade neutropenia. In this prospective, bicentric clinical trial, we evaluated the palbociclib exposure−toxicity relationship and determined the relevant sources of palbociclib pharmacokinetic variability, including drug−drug interactions (DDI). We followed 58 patients (mean age: 62.9 years) for 1 year. The geometric median of palbociclib plasma trough concentration (Ctrough) was 74.1 ng/mL. Neutropenia occurred in 70.7% of patients (high grade in 67.2% of patients). High-grade neutropenia occurrence during the first two palbociclib cycles was higher in patients with lower neutrophil count at initiation (p = 0.002). Palbociclib plasma Ctrough was correlated with high-grade neutropenia occurrence during the first two cycles (p = 0.024, OR 5.51). Co-treatment with agents that may interfere with palbociclib PK significantly influenced palbociclib Ctrough (p < 0.05). CYP3A4/P-glycoprotein inhibitors increased by 25% palbociclib Ctrough (p = 0.035), while antacids reduced it by 20% (p = 0.036). However, DDI did not have any significant effect on high-grade neutropenia occurrence (p > 0.05). This study confirms the major role of TDM to manage palbociclib safe use from the first week of treatment, particularly the significant incidence of hematological toxicity. Moreover, this first dedicated prospective study confirmed the importance of characterizing co-treatments to limit the DDI risk with oral-targeted therapies.

A phase II trial of an alternative schedule of palbociclib and embedded serum TK1 analysis

Palbociclib 3-weeks-on/1-week-off, combined with hormonal therapy, is approved for hormone receptor positive (HR+)/HER2-negative (HER2-) advanced/metastatic breast cancer (MBC). Neutropenia is the most frequent adverse event (AE). We aim to determine whether an alternative 5-days-on/2-days-off weekly schedule reduces grade 3 and above neutropenia (G3 + ANC) incidence. In this single-arm phase II trial, patients with HR+/HER2- MBC received palbociclib 125 mg, 5-days-on/2-days-off, plus letrozole or fulvestrant per physician, on a 28-day cycle (C), as their first- or second-line treatment. The primary endpoint was G3 + ANC in the first 29 days (C1). Secondary endpoints included AEs, efficacy, and serum thymidine kinase 1 (sTK1) activity. At data-cutoff, fifty-four patients received a median of 13 cycles (range 2.6-43.5). The rate of G3 + ANC was 21.3% (95% CI: 11.2-36.1%) without G4 in C1, and 40.7% (95% CI: 27.9-54.9%), including 38.9% G3 and 1.8% G4, in all cycles. The clinical benefit rate was 80.4% (95% CI: 66.5-89.7%). The median progression-free survival (mPFS) (95% CI) was 19.75 (12.11-34.89), 33.5 (17.25-not reached [NR]), and 11.96 (10.43-NR) months, in the overall, endocrine sensitive or resistant population, respectively. High sTK1 at baseline, C1 day 15 (C1D15), and C2D1 were independently prognostic for shorter PFS (p = 9.91 × 10-4, 0.001, 0.007, respectively). sTK1 decreased on C1D15 (p = 4.03 × 10-7), indicating target inhibition. Rise in sTK1 predicted progression, with the median lead time of 59.5 (inter-quartile range: -206.25-0) days. Palbociclib, 5-days-on/2-days-off weekly, met its primary endpoint with reduced G3 + ANC, without compromising efficacy. sTK1 is prognostic and shows promise in monitoring the palbociclib response. ClinicalTrials.gov#: NCT3007979.

Incidence and Severity of Myelosuppression With Palbociclib After Palliative Bone Radiation in Advanced Breast Cancer: A Single Center Experience and Review of Literature

BACKGROUND

Palbociclib is a cyclin-dependent kinase (CDK) 4/6 inhibitor with a primary toxicity of myelosuppression, especially neutropenia, due to cytostatic CDK6 inhibition on bone marrow. Preclinical studies suggest palbociclib may enhance radiation toxicity, but this was only evaluated in limited case series of palliative radiotherapy and not specific to radiation targeting bony metastases.

PATIENTS AND METHODS

This was a single institution retrospective cohort study. We included female patients who initiated palbociclib for advanced breast cancer between 2015 and 2019. The primary exposure was receipt of palliative radiation to bony metastases within 1 year prior to starting palbociclib. The primary outcome was the incidence and severity of myelosuppression during cycle one. Secondary outcomes include treatment interruptions and cycle 2 dose reductions, with subgroup analysis of radiation timing, type, dose, and location.

RESULTS

Of the 247 patients, 47 received radiation to bone metastases. Only absolute lymphocyte count (ALC) after cycle one of palbociclib was significantly lower in the group receiving radiation (median ALC 0.84 vs. 1.10 K/mm³, P < .001), with similar rates of neutropenia, anemia, and thrombocytopenia. Patients who received ≥10 fractions radiation were more likely to have cycle one interrupted than those receiving shorter radiation courses (42.9% vs. 11.1%, P = .03). No radiation characteristics were associated with other hematologic toxicities or dose reduction.

CONCLUSION

Palliative bone radiation within 1 year prior to palbociclib initiation was associated with greater lymphopenia during the first cycle than patients unexposed to radiation, but not neutropenia, anemia, or thrombocytopenia that would modify treatment.

Integrating CDK4/6 inhibitors in the treatment of patients with early breast cancer

CDK4/6 inhibitors have an established role in the treatment of hormone receptor positive HER2-negative advanced breast cancer. All studies conducted in metastatic breast cancer showed a benefit in delaying progression when added to standard endocrine therapy, regardless of therapy line, pretreatment, menopausal status, site of metastasis, CDK4/6 inhibitor used and associated endocrine therapy. A benefit in overall survival has also been demonstrated. In early breast cancer, only the MonarchE study has shown an improved invasive disease-free survival with abemaciclib taken for 2 years, whereas the Penelope-B did not meet the primary endpoint and the PALLAS study was terminated early for futility. Studies conducted in the neoadjuvant setting might help to explain the discordant results.

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CDK4/6 inhibitors increase PFS in advanced breast cancer in all subgroups.

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2-years abemaciclib added to endocrine therapy improves invasive disease-free survival in high-risk breast cancer.

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Palbociclib did not improve invasive disease-free survival in early breast cancer.

Real-World Data of Palbociclib in Combination With Endocrine Therapy for the Treatment of Metastatic Breast Cancer in Men

This report examined the benefits and risks of palbociclib plus endocrine therapy (ET) in men with hormone receptor-positive (HR+)/human epidermal growth factor receptor 2-negative (HER2-) metastatic breast cancer (MBC). Palbociclib was evaluated using three independent data sources: real-world data from pharmacy and medical claims, a de-identified real-world data source derived from electronic health records (EHRs), and a global safety database. From medical and pharmacy records, 1,139 men with MBC were identified; in the first-line setting, median duration of treatment was longer with palbociclib plus ET (n = 37, 8.5 months, 95% confidence interval (CI), 4.4-13.0) than ET alone (n = 214, 4.3 months, 95% CI, 3.0-5.7) and specifically, was longer with palbociclib plus letrozole (n = 26, 9.4 months, 95% CI, 4.4-14.0) than letrozole alone (n = 63, 3.0 months, 95% CI, 1.8-4.8). In the EHR-derived database, 59 men received treatment for MBC; real-world response across all lines of therapy in the metastatic setting was reported in 4 of 12 patients (33.3%) in the palbociclib plus ET group vs. 1 of 8 (12.5%) patients in the ET group. Review of the global safety database did not identify any new safety signals in palbociclib-treated men. Real-world data indicated that men with MBC benefit from palbociclib plus ET, with a safety profile consistent with previous observations in women with MBC. Collective data on palbociclib in women and men in this report, including clinical trial data, real-world data, and a well-established risk/benefit profile, led to US approval of an expansion of the palbociclib indication to include men with MBC.

Predictors for development of palbociclib-induced neutropenia in breast cancer patients as determined by ordered logistic regression analysis

This retrospective study aimed to identify predictors for the development of palbociclib-induced neutropenia. This study retrospectively analysed 78 breast cancer patients who had received palbociclib at our hospital between January 2018 and May 2020. For the regression analysis of factors associated with palbociclib-induced neutropenia, variables were extracted manually from medical charts. The level of palbociclib-induced neutropenia was evaluated using the National Cancer Institute’s Common Terminology Criteria for Adverse Events (version 5). Multivariate ordered logistic regression analysis was performed to identify predictors for the development of neutropenia. Optimal cut-off thresholds were determined using receiver operating characteristic (ROC) analysis. Values of P < 0.05 (2-tailed) were considered significant. Significant factors identified included concomitant use of statin (odds ratio [OR] = 0.104, 95% confidence interval [CI] = 0.018–0.598; P = 0.011) and body mass index (BMI) (OR = 1.118, 95% CI = 1.007–1.241; P = 0.037). ROC analysis revealed that neutropenia (grade 4) was more likely to occur with a BMI ≥ 22.3 kg/m². In conclusion, no concomitant use of statins and high BMI were identified as significant predictors for the development of palbociclib-induced neutropenia.

Endocrine Treatment and Targeted Therapy for Hormone Receptor-Positive, Human Epidermal Growth Factor Receptor 2-Negative Metastatic Breast Cancer: ASCO Guideline Update

PURPOSE

To update recommendations of the ASCO systemic therapy for hormone receptor (HR)-positive metastatic breast cancer (MBC) guideline.

METHODS

An Expert Panel conducted a systematic review to identify new, potentially practice-changing data.

RESULTS

Fifty-one articles met eligibility criteria and form the evidentiary basis for the recommendations.

RECOMMENDATIONS

Alpelisib in combination with endocrine therapy (ET) should be offered to postmenopausal patients, and to male patients, with HR-positive, human epidermal growth factor receptor 2 (HER2)-negative, PIK3CA-mutated, ABC, or MBC following prior endocrine therapy with or without a cyclin-dependent kinase (CDK) 4/6 inhibitor. Clinicians should use next-generation sequencing in tumor tissue or cell-free DNA in plasma to detect PIK3CA mutations. If no mutation is found in cell-free DNA, testing in tumor tissue, if available, should be used as this will detect a small number of additional patients with PIK3CA mutations. There are insufficient data at present to recommend routine testing for ESR1 mutations to guide therapy for HR-positive, HER2-negative MBC. For BRCA1 or BRCA2 mutation carriers with metastatic HER2-negative breast cancer, olaparib or talazoparib should be offered in the 1st-line through 3rd-line setting. A nonsteroidal aromatase inhibitor (AI) and a CDK4/6 inhibitor should be offered to postmenopausal women with treatment-naïve HR-positive MBC. Fulvestrant and a CDK4/6 inhibitor should be offered to patients with progressive disease during treatment with AIs (or who develop a recurrence within 1 year of adjuvant AI therapy) with or without one line of prior chemotherapy for metastatic disease, or as first-line therapy. Treatment should be limited to those without prior exposure to CDK4/6 inhibitors in the metastatic setting.Additional information can be found at www.asco.org/breast-cancer-guidelines.

Clinical considerations of CDK4/6 inhibitors in triple-negative breast cancer

The formation of cyclinD-CDK4/6 complex plays vital roles in the cell cycle transition from G1 phase to S phase which is characterized by vigorous transcription and synthesis. Through cyclinD-CDK4/6-Rb axis, CDK4/6 inhibitors arrest the cell cycle in the G1 phase and block the proliferation of aggressive cells, exhibiting promising effects in containing the aggressiveness of breast cancers. To date, there are three CDK4/6 inhibitors approved by the U.S. Food and Drug Administration in treating advanced hormone receptor-positive breast cancer, including palbociclib, abemaciclib, and ribociclib. In fact, several preclinical experiments and clinical trials presented therapeutic effects of CDK4/6 inhibitor-based treatment in triple-negative breast cancer.

Clinical and Pharmacologic Differences of CDK4/6 Inhibitors in Breast Cancer

Targeted therapies such as Cyclin Dependent Kinase 4 and 6 (CDK 4/6) inhibitors have improved the prognosis of metastatic hormone receptor (HR) positive breast cancer by combating the resistance seen with traditional endocrine therapy. The three approved agents currently in the market are palbociclib, ribociclib and abemaciclib. Besides the overall similarities associated with CDK4/6 inhibition, there are differences between the three approved agents that may explain the differences noted in unique clinical scenarios- monotherapy, patients with brain metastases or use in the adjuvant setting. This review article will explore the preclinical and pharmacological differences between the three agents and help understand the benefits seen with these agents in certain subgroups of patients with metastatic HR positive breast cancer.

Hematologic safety of palbociclib in combination with endocrine therapy in patients with benign ethnic neutropenia and advanced breast cancer

BACKGROUND

Cyclin-dependent kinase 4/6 (CDK4/6) inhibitors, including palbociclib, are approved to treat hormone receptor (HR)-positive/human epidermal growth factor receptor 2 (HER2)-negative advanced breast cancer (ABC) and are associated with hematologic toxicity. African American women, who are underrepresented in CDK4/6 inhibitor clinical trials, may experience worse neutropenia because of benign ethnic neutropenia. The authors specifically investigated the hematologic safety of palbociclib in African American women with HR-positive/HER2-negative ABC.

METHODS

PALINA was a single-arm, open-label, investigator-initiated study of palbociclib (125 mg daily; 21 days on and 7 days off) plus endocrine therapy (ET) in African American women who had HR-positive/HER2-negative ABC and a baseline absolute neutrophil count ≥1000/mm³ (ClinicalTrials.gov identifier NCT02692755). The primary outcome was the proportion of patients who completed 12 months of therapy without experiencing febrile neutropenia or treatment discontinuation because of neutropenia. Single nucleotide polymorphism analysis was used to assess Duffy polymorphism status.

RESULTS

Thirty-five patients received ≥1 dose of palbociclib plus ET; 19 had a Duffy null polymorphism (cytosine/cytosine). There were no reports of febrile neutropenia or permanent study discontinuation because of neutropenia. Significantly more patients with the Duffy null versus the wild-type variant had grade 3 and 4 neutropenia (72.2% vs 23.1%; P = .029) and required a palbociclib dose reduction (55.6% vs 7.7%; P = .008). Patients with the Duffy null versus the wild-type variant had lower overall relative dose intensity (mean ± SD, 81.89% ± 15.87 and 95.67% ± 5.89, respectively; P = .0026) and a lower clinical benefit rate (66.7% and 84.6%, respectively).

CONCLUSIONS

These findings suggest that palbociclib is well tolerated in African American women with HR-positive/HER2-negative ABC. Duffy null status may affect the incidence of grade 3 neutropenia, dose intensity, and possibly clinical benefit.

Evaluation of the Association of Polymorphisms With Palbociclib-Induced Neutropenia: Pharmacogenetic Analysis of PALOMA-2/-3

BACKGROUND

The most frequently reported treatment-related adverse event in clinical trials with the cyclin-dependent kinase 4/6 (CDK4/6) inhibitor palbociclib is neutropenia. Allelic variants in ABCB1 and ERCC1 might be associated with early occurrence (i.e., end of week 2 treatment) of grade 3/4 neutropenia. Pharmacogenetic analyses were performed to uncover associations between single nucleotide polymorphisms (SNPs) in these genes, patient baseline characteristics, and early occurrence of grade 3/4 neutropenia.

MATERIALS AND METHODS

ABCB1 (rs1045642, rs1128503) and ERCC1 (rs3212986, rs11615) were analyzed in germline DNA from palbociclib-treated patients from PALOMA-2 (n = 584) and PALOMA-3 (n = 442). SNP, race, and cycle 1 day 15 (C1D15) absolute neutrophil count (ANC) data were available for 652 patients. Univariate and multivariable analyses evaluated associations between SNPs, patient baseline characteristics, and early occurrence of grade 3/4 neutropenia. Analyses were stratified by Asian (n = 122) and non-Asian (n = 530) ethnicity. Median progression-free survival (mPFS) was estimated using the Kaplan-Meier method. The effect of genetic variants on palbociclib pharmacokinetics was analyzed.

RESULTS

ABCB1 and ERCC1_rs11615 SNP frequencies differed between Asian and non-Asian patients. Multivariable analysis showed that low baseline ANC was a strong independent risk factor for C1D15 grade 3/4 neutropenia regardless of race (Asians: odds ratio [OR], 6.033, 95% confidence interval [CI], 2.615-13.922, p < .0001; Non-Asians: OR, 6.884, 95% CI, 4.138-11.451, p < .0001). ABCB1_rs1128503 (C/C vs. T/T: OR, 0.57, 95% CI, 0.311-1.047, p = .070) and ERCC1_rs11615 (A/A vs. G/G: OR, 1.75, 95% CI, 0.901-3.397, p = .098) were potential independent risk factors for C1D15 grade 3/4 neutropenia in non-Asian patients. Palbociclib mPFS was consistent across genetic variants; exposure was not associated with ABCB1 genotype.

CONCLUSION

This is the first comprehensive assessment of pharmacogenetic data in relationship to exposure to a CDK4/6 inhibitor. Pharmacogenetic testing may inform about potentially increased likelihood of patients developing severe neutropenia (NCT01740427, NCT01942135).

IMPLICATIONS FOR PRACTICE

Palbociclib plus endocrine therapy improves hormone receptor-positive/human epidermal growth factor receptor 2-negative advanced breast cancer outcomes, but is commonly associated with neutropenia. Genetic variants in ABCB1 may influence palbociclib exposure, and in ERCC1 are associated with chemotherapy-induced severe neutropenia. Here, the associations of single nucleotide polymorphisms in these genes and baseline characteristics with neutropenia were assessed. Low baseline absolute neutrophil count was a strong risk factor (p < .0001) for grade 3/4 neutropenia. There was a trend indicating that ABCB1_rs1128503 and ERCC1_rs11615 were potential risk factors (p < .10) for grade 3/4 neutropenia in non-Asian patients. Pharmacogenetic testing could inform clinicians about the likelihood of severe neutropenia with palbociclib.

CDK4/6 Inhibitors and Arthralgia: A Single Institution Experience

Background: Aromatase inhibitors (AIs) are associated with musculoskeletal pain in one third (20–47%) of breast cancer patients. Recently, CDK4/6 inhibitors have emerged as a new therapeutic approach in hormone receptor (HR)-positive breast cancer. While hematological and gastrointestinal toxicities are frequently reported during treatment with CDK4/6 inhibitors, musculoskeletal symptoms are less commonly encountered. Methods: Herein, we present a retrospective study of 47 breast cancer patients who received CDK4/6 inhibitors along with endocrine therapy in our department between 01/01/2018 and 01/09/2020. Results: Median age at diagnosis was 58 years (29–81). Median duration of treatment was 8.76 months (SD: 7.68; 0.47–30.13 months). Median PFS was 24.33 months (95% CI; 1.71–46.96). Overall, toxicity was reported in 61.7% of the cases (29/47). Arthralgia was reported in 6.4% (3/47) of the patients. Hematological toxicity was reported in 51.1% (24/47) of the patients. Neutropenia was the main hematological toxicity observed (86.8%; 22/47) along with anemia (4.3%; 2/47), thrombocytopenia (2.1%; 1/47), and leukopenia (4.2%; 1/24). Conclusions: Though our data reflect a small sample size, we report a reduced arthralgia rate (6.4%) during treatment with CDK4/6 inhibitors compared with that reported in studies of AIs (20–47%).

Targeting Nuclear Receptors for Cancer Therapy: Premises, Promises, and Challenges

Nuclear receptors are a family of transcription factors localized in cell nuclei, sensing specific ligands and fine-tuning a variety of cell physiological events. They have been intensively investigated in cancer biology. With their excellent properties of druggability and actionability, nuclear receptors have demonstrated much promise as novel therapeutic targets for different cancer types. Accumulating evidence has highlighted the essential roles of certain nuclear receptors in tumor immunology, suggesting the possibility for them to serve as cancer immunotherapeutic targets. Here, we summarize the roles of nuclear receptors in cancer biology and tumor immunology, and underscore the current advances of clinical trials for nuclear receptor-based cancer therapeutics.

[Patients treated with palbociclib and endocrine therapy for metastatic breast cancer: Can we predict the occurrence of severe early hematological toxicity?]

INTRODUCTION

The addition of palbociclib to endocrine therapy has been shown to improve progression free survival in hormone receptor positive metastatic breast cancer patients. This cyclin CDK4/6 inhibitor could expose patients to a grade 3-4 hematological toxicity, leading to treatment discontinuation or treatment interruption that is potentially associated with a lack of efficiency. The aim of this study was to identify predictive factors of severe early hematotoxicity (ESHT).

METHODS

This retrospective cohort study included patients who started palbociclib in the Institut Sainte Catherine between December 1, 2016 and January 1, 2019 for the treatment of metastatic breast cancer. Individual data and hematological toxicity were collected from electronic medical records. ESHT was defined as the occurrence, during the first 3 cycles, of grade 4 or grade 3 hematological toxicity requiring palbociclib dose reduction.

RESULTS

In total, 181 patients (180 females) were included; median age was 67 years. Forty-six patients (25.4%) experienced an ESHT. Predictive factors of ESHT in multivariate analysis were a performance status (PS) of 2 or more (P=0.024) and an history of radiotherapy of bone metastasis in the previous year (P=0.003). Before palbociclib initiation, a neutrophil count below 3.37g/L was predictive of ESHT with a sensibility of 76% and a specificity of 71%.

CONCLUSIONS

ECOG PS, bone radiotherapy within the year and low baseline neutrophils count are associated with ESHT in palbociclib-treated metastatic breast cancer patients. These elements could be useful for a careful monitoring leading to adapted therapy.

First clinical experience with CDK4/6 inhibitors in breast cancer therapy

For hormone receptor-positive, HER2-negative breast cancer patients with metastatic or advanced disease, therapy with CDK4/6 inhibitors in addition to aromatase inhibitors (AIs) or to the estrogen receptor (ER) downregulator fulvestrant has resulted in an additional therapy option and a longer progression-free survival. In the Gynecologic-Oncology Clinic, Diakonie-Klinikum Schwäbisch Hall, we followed and registered our initial clinical experience with CDK4/6 inhibitors, following the side effects and tumor response over two years since they were officially approved for general use in Germany. Differences were observed when palbociclib or ribociclib was used in combination with letrozole or anastrozole or fulvestrant. The dynamic side effects and tumor response under therapy with palbociclib or ribociclib were found to be comparable with the main reported data in the official drug information. The CDK4/6 inhibitors have an important and promising role in the therapy of breast cancer patients. Patient age and therapy duration do not influence the use of palbociclib or ribociclib, although it may be important which AI is used in combination with palbociclib.

Long-Term Pooled Safety Analysis of Palbociclib in Combination with Endocrine Therapy for Hormone Receptor-Positive/Human Epidermal Growth Factor Receptor 2-Negative Advanced Breast Cancer: Updated Analysis with up to 5 Years of Follow-Up

Background

Previous studies demonstrated the tolerability of palbociclib plus endocrine therapy (ET). This analysis evaluated safety based on more recent cutoff dates and a longer palbociclib treatment exposure.

Patients and Methods

Data were pooled from three randomized studies of patients with hormone receptor‐positive/human epidermal growth factor receptor 2‐negative (HR+/HER2−) advanced breast cancer (ABC), including postmenopausal women who had not received prior systemic treatment for advanced disease (PALOMA‐1/‐2) and pre‐ and postmenopausal women who had progressed on prior ET (PALOMA‐3).

Results

Updated cutoff dates were December 21, 2017 (PALOMA‐1), May 31, 2017 (PALOMA‐2), and April 13, 2018 (PALOMA‐3). Total person‐years of treatment exposure were 1,421.6 with palbociclib plus ET (n = 872) and 528.4 with ET (n = 471). Any‐grade neutropenia and infections were more frequent with palbociclib plus ET (82.1% and 59.2%, respectively) than with ET (5.1% and 39.5%). The hazard ratios were 1.6 (p = .0995) for grade 3/4 infections, 1.8 (p = .4358) for grade 3/4 viral infections, 1.4 (p = .0001) for infections, and 30.8 (p < .0001) for neutropenia. Febrile neutropenia was reported in 1.4% of patients receiving palbociclib plus ET. Cumulative incidence of all‐grade hematologic adverse events in both arms peaked during the first year of treatment and plateaued over the 5 subsequent years. Interstitial lung disease was reported in 13 patients receiving palbociclib plus ET and 3 receiving ET.

Conclusion

This 5‐year, long‐term analysis demonstrated that palbociclib plus ET has a consistent and stable safety profile and is a safe treatment for patients with HR+/HER2− ABC.

Implications for Practice

Several treatments for patients with breast cancer are associated with long‐term or latent adverse events. This long‐term, 5‐year analysis demonstrated that palbociclib plus endocrine therapy has a consistent and stable safety profile without cumulative or delayed toxicities. These results further support palbociclib plus endocrine therapy as a safe and manageable treatment in clinical practice for patients with hormone receptor‐positive/human epidermal growth factor receptor 2‐negative advanced breast cancer.

This updated analysis based on data pooled from the three PALOMA studies is the largest long‐term analysis, to date, of the safety of a CDK4/6 inhibitor in combination with endocrine therapy for the treatment of advanced breast cancer.

Real-world safety of palbociclib in breast cancer patients in the United States: a new user cohort study

Background

There is limited real-world safety information on palbociclib for treatment of advanced stage HR+/HER2- breast cancer.

Methods

We conducted a cohort study of breast cancer patients initiating palbociclib and fulvestrant from February 2015 to September 2017 using the HealthCore Integrated Research Database (HIRD), a longitudinal claims database of commercial health plan members in the United States.

The historical comparator cohort comprised patients initiating fulvestrant monotherapy from January 2011 to January 2015. Propensity score matching and Cox regression were used to estimate hazard ratios for various safety events. For acute liver injury (ALI), additional analyses and medical record validation were conducted.

Results

There were 2445 patients who initiated palbociclib including 566 new users of palbociclib-fulvestrant, and 2316 historical new users of fulvestrant monotherapy. Compared to these historical new users of fulvestrant monotherapy, new users of palbociclib-fulvestrant had a greater than 2-fold elevated risk for neutropenia, leukopenia, thrombocytopenia, stomatitis and mucositis, and ALI. Incidence of anemia and QT prolongation were more weakly associated, and incidences of serious infections and pulmonary embolism were similar between groups after propensity score matching. After adjustment for additional ALI risk factors, the elevated risk of ALI in new users of palbociclib-fulvestrant persisted (e.g. primary ALI algorithm hazard ratio (HR) = 3.0, 95% confidence interval (CI) = 1.1–8.4).

Conclusions

This real-world study found increased risks of several adverse events identified in clinical trials, including neutropenia, leukopenia, and thrombocytopenia, but no increased risk of serious infections or pulmonary embolism when comparing new users of palbociclib-fulvestrant to fulvestrant monotherapy. We observed an increased risk of ALI, extending clinical trial findings of significant imbalances in grade 3/4 elevations of alanine aminotransferase (ALT).

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-021-07790-z.

Do we still need breast cancer screening in the era of targeted therapies and precision medicine?

Breast cancer (BC) is the most common female cancer and the second cause of death among women worldwide. The 5-year relative survival rate recently improved up to 90% due to increased population coverage and women's attendance to organised mammography screening as well as to advances in therapies, especially systemic treatments. Screening attendance is associated with a mortality reduction of at least 30% and a 40% lower risk of advanced disease. The stage at diagnosis remains the strongest predictor of recurrences. Systemic treatments evolved dramatically over the last 20 years: aromatase inhibitors improved the treatment of early-stage luminal BC; targeted monoclonal antibodies changed the natural history of anti-human epidermal growth factor receptor 2-positive (HER2) disease; immunotherapy is currently investigated in patients with triple-negative BC; gene expression profiling is now used with the aim of personalising systemic treatments. In the era of precision medicine, it is a challenging task to define the relative contribution of early diagnosis by screening mammography and systemic treatments in determining BC survival. Estimated contributions before 2000 were 46% for screening and 54% for treatment advances and after 2000, 37% and 63%, respectively. A model showed that the 10-year recurrence rate would be 30% and 25% using respectively chemotherapy or novel treatments in the absence of screening, but would drop to 19% and 15% respectively if associated with mammography screening. Early detection per se has not a curative intent and systemic treatment has limited benefit on advanced stages. Both screening mammography and systemic therapies continue to positively contribute to BC prognosis.

CDK4/6 Inhibitors in Breast Cancer Treatment: Potential Interactions with Drug, Gene, and Pathophysiological Conditions

Palbociclib, ribociclib, and abemaciclib belong to the third generation of cyclin-dependent kinases inhibitors (CDKis), an established therapeutic class for advanced and metastatic breast cancer. Interindividual variability in the therapeutic response of CDKis has been reported and some individuals may experience increased and unexpected toxicity. This narrative review aims at identifying the factors potentially concurring at this variability for driving the most appropriate and tailored use of CDKis in the clinic. Specifically, concomitant medications, pharmacogenetic profile, and pathophysiological conditions could influence absorption, distribution, metabolism, and elimination pharmacokinetics. A personalized therapeutic approach taking into consideration all factors potentially contributing to an altered pharmacokinetic/pharmacodynamic profile could better drive safe and effective clinical use.

Optimizing Palbociclib Therapy Across the Age Spectrum: Hypothetical, Illustrative Case Scenarios in HR+, HER2-Metastatic Breast Cancer

Cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors in combination with endocrine therapy are a preferred treatment option for premenopausal and postmenopausal women with hormone receptor–positive (HR+), human epidermal growth factor receptor 2–negative (HER2–) metastatic breast cancer (mBC). Palbociclib is a potent, first-in-class oral inhibitor of CDK4/6. To provide optimal care to patients with HR+/HER2– mBC receiving palbociclib, advanced practitioners require a thorough understanding of the efficacy and adverse event (AE) profile of palbociclib as well as the diverse characteristics and support needs of patients eligible for palbociclib treatment. This Grand Rounds uses two hypothetical patient scenarios to illustrate core issues in the management of premenopausal and postmenopausal patients receiving palbociclib-based therapy for mBC. In addition to providing an overview of key efficacy and safety data, each case offers practical guidance on providing individualized, patient-centered care, the identification and management of treatment-related AEs, management of concomitant medications, and best practices to promote adherence to therapy.

Overall survival results from the randomized phase 2 study of palbociclib in combination with letrozole versus letrozole alone for first-line treatment of ER+/HER2- advanced breast cancer (PALOMA-1, TRIO-18)

PURPOSE

Palbociclib is a cyclin-dependent kinase 4/6 (CDK4/6) inhibitor, approved in combination with endocrine therapy for the treatment of women and men with hormone receptor-positive, human epidermal growth factor receptor 2-negative advanced breast cancer (HR+/HER2- ABC). In the phase 2, open-label, PALOMA-1 trial, palbociclib plus letrozole significantly prolonged progression-free survival (PFS) versus letrozole alone (hazard ratio, 0.488; 95% CI 0.319‒0.748; P = 0.0004; median PFS, 20.2 vs 10.2 months, respectively) in postmenopausal women with estrogen receptor-positive (ER+)/HER2- ABC. Here, we present the final overall survival (OS) and updated safety results.

METHODS

Postmenopausal women with ER+/HER2- ABC were randomized 1:1 to receive either palbociclib (125 mg/day, 3/1 schedule) plus letrozole (2.5 mg/day, continuous) or letrozole alone (2.5 mg/day, continuous). The primary endpoint was investigator-assessed PFS; secondary endpoints included OS and safety.

RESULTS

A total of 165 patients were randomized. At the data cutoff date of December 30, 2016 (median duration of follow-up, 64.7 months), the stratified hazard ratio for OS was 0.897 (95% CI 0.623-1.294; P = 0.281); median OS in the palbociclib plus letrozole and letrozole alone arms was 37.5 and 34.5 months, respectively. The median time from randomization to first subsequent chemotherapy use was longer with palbociclib plus letrozole than letrozole alone (26.7 and 17.7 months, respectively). The most frequently reported adverse event in the palbociclib plus letrozole arm was neutropenia (any grade, 75%; grade 3 or 4, 59%).

CONCLUSIONS

Palbociclib plus letrozole treatment led to a numerical but not statistically significant improvement in median OS. Pfizer Inc (NCT00721409).

Clinical implications of prospective genomic profiling of metastatic breast cancer patients

Background

Metastatic breast cancer remains incurable. Next-generation sequencing (NGS) offers the ability to identify actionable genomic alterations in tumours which may then be matched with targeted therapies, but the implementation and utility of this approach is not well defined for patients with metastatic breast cancer.

Methods

We recruited patients with advanced breast cancer of any subtype for prospective targeted NGS of their most recent tumour samples, using a panel of 108 breast cancer-specific genes. Genes were classified as actionable or non-actionable using the European Society of Medical Oncology Scale for Clinical Actionability of Molecular Targets (ESCAT) guidelines.

Results

Between February 2014 and May 2019, 322 patients were enrolled onto the study, with 72% (n = 234) of patients successfully sequenced (n = 357 samples). The majority (74%, n = 171) of sequenced patients were found to carry a potentially actionable alteration, the most common being a PIK3CA mutation. Forty-three percent (n = 74) of patients with actionable alterations were referred for a clinical trial or referred for confirmatory germline testing or had a change in therapy outside of clinical trials. We found alterations in AKT1, BRCA2, CHEK2, ESR1, FGFR1, KMT2C, NCOR1, PIK3CA and TSC2 to be significantly enriched in our metastatic population compared with primary breast cancers. Concordance between primary and metastatic samples for key driver genes (TP53, ERBB2 amplification) was > 75%. Additionally, we found that patients with a higher number of mutations had a significantly worse overall survival.

Conclusion

Genomic profiling of patients with metastatic breast cancer can have clinical implications and should be considered in all suitable patients.

Assessing the Impact of the COVID-19 Outbreak on the Attitudes and Practice of Italian Oncologists Toward Breast Cancer Care and Related Research Activities

PURPOSE

To investigate the impact of the COVID-19 outbreak on the attitudes and practice of Italian oncologists toward breast cancer care and related research activities.

METHODS

A 29-question anonymous online survey was sent by e-mail to members of the Italian Association of Medical Oncology and the Italian Breast Cancer Study Group on April 3, 2020. Only medical oncologists (both those in training and specialists) were invited to complete the questionnaire.

RESULTS

Out of 165 responding oncologists, 121 (73.3.%) worked in breast units. In the (neo)adjuvant setting, compared with before the emergency, fewer oncologists adopted weekly paclitaxel (68.5% v 93.9%) and a dose-dense schedule for anthracycline-based chemotherapy (43% v 58.8%) during the COVID-19 outbreak. In the metastatic setting, compared with before the emergency, fewer oncologists adopted first-line weekly paclitaxel for HER2-positive disease (41.8% v 53.9%) or CDK4/6 inhibitors for luminal tumors with less-aggressive characteristics (55.8% v 80.0%) during the COVID-19 outbreak. A significant change was also observed in delaying the timing for monitoring therapy with CDK4/6 inhibitors, assessing treatment response with imaging tests, and flushing central venous devices. Clinical research and scientific activities were reduced in 80.3% and 80.1% of respondents previously implicated in these activities, respectively.

CONCLUSION

Medical oncologists face many challenges in providing cancer care during the COVID-19 outbreak. Although most of the changes in their attitudes and practice were reasonable responses to the current health care emergency without expected major negative impact on patient outcomes, some potentially alarming signals of undertreatment were observed.

RENATA study-Latin American prospective experience: clinical outcome of patients treated with palbociclib in hormone receptor-positive metastatic breast cancer-real-world use

Background

In hormone receptor-positive, HER-2 negative (HR+/HER2-) advanced breast cancer (ABC) endocrine therapy (ET) plus cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) in first and second line improved progression-free survival (PFS), overall response rate (ORR) and clinical benefit rate (CB) without deterioration in quality of life compared with ET alone. In addition, recent data showed improvement in overall survival (OS) for premenopausal women in first line setting and for different subgroups of patients in second line. Since 2015, in Argentina, the combination of ET with CDK4/6i is a standard of care in HR+/HER2- ABC.

Methods

We carried out a prospective analysis of real-world use of palbociclib with ET in HR+/HER2- ABC patients who received treatment between October 2015 and August 2019 in two private institutes from Buenos Aires, Argentina. The aims of the study were to determine efficacy and safety of patients treated with ET and palbociclib, describe patient profile and treatment strategy beyond progression.

Results

One-hundred and twenty-eight patients were included in the final analysis. Main baseline characteristics include, median age 57 years, 20% were premenopausal women, 44% had visceral metastasis and 26% bone only disease. More than half of patients had two or more metastatic sites, 44.4% had performance status 1, and most of them (59.4%) were treated with palbociclib in first-line setting. Palbociclib was preferentially associated with aromatase inhibitors in 63.9% of patients, and with fulvestrant in the remaining. All premenopausal women received ovarian suppression or ovarian ablation (OS/OA). The median PFS was 36.7 months in first line and 24.2 months in second line. The ORR was 45.3% and 25.0% in first and second line, respectively. The median OS in the entire population was not reached. Half of patients did not require dose interruption and/or delay, dose reduction was required in 15% of patients and almost no patients required drug discontinuation (2.0%). With regard to safety, 55% of patients developed grade 3-4 adverse events, 20% neutropenia grade 3-4, and 7% febrile neutropenia. Infections were presented in one out of three patients, mostly uncomplicated.

Conclusions

This is the first prospective evidence of real-world use of palbociclib in a Latin American population. We found similar outcomes to the PALOMA-2 and PALOMA-3 randomised trials and Real-World Data already published, with lower incidence of side effects and treatment discontinuation, but with higher incidence of febrile neutropenia.

Grade 3 Hepatotoxicity following Fulvestrant, Palbociclib, and Erdafitinib Therapy in a Patient with ER-Positive/PR-Negative/HER2-Negative Metastatic Breast Cancer: A Case Report

A 49-year-old woman with ER-positive/PR-negative/HER2-negative metastatic breast cancer experienced Grade 3 hepatotoxicity following initiation of a clinical trial of fulvestrant, palbociclib, and erdafitinib. Fulvestrant was determined to be the drug most likely responsible for this hepatotoxic effect. This case report details the timing and nature of this drug-induced liver injury, adding support to an area that has yet to be described adequately in the existing literature.

Hematologic adverse events following palbociclib dose reduction in patients with hormone receptor-positive/human epidermal growth factor receptor 2-negative advanced breast cancer: pooled analysis from randomized phase 2 and 3 studies

BACKGROUND

Palbociclib improves outcomes for women with hormone receptor-positive/human epidermal growth factor receptor 2-negative advanced breast cancer (HR+/HER2- ABC). Dose reductions are recommended for the management of hematologic toxicities. A previous pooled analysis from the PALOMA clinical trials showed that 36.9% of patients required dose reduction, predominantly during the first 6 months of treatment and with decreasing frequency during subsequent 28-day treatment cycles (C). Previous data have shown that palbociclib dose reductions do not affect efficacy. This pooled, post hoc analysis evaluated the frequency of hematologic adverse events (AEs) before and after palbociclib dose reduction in PALOMA-1, PALOMA-2, and PALOMA-3.

METHODS

This analysis evaluated the frequency of hematologic AEs 30 days before dose reduction and during each subsequent treatment from C1 to C6 among patients who required palbociclib dose reduction. Data were pooled from 3 randomized studies. PALOMA-1 was a phase 2, open-label study of postmenopausal patients untreated for ABC receiving palbociclib plus letrozole or letrozole alone. PALOMA-2 was a phase 3, double-blind study of postmenopausal patients untreated for ABC receiving palbociclib plus letrozole or placebo plus letrozole. PALOMA-3 was a phase 3, double-blind study of pre/perimenopausal or postmenopausal patients, whose disease progressed on prior endocrine therapy, receiving palbociclib plus fulvestrant or placebo plus fulvestrant.

RESULTS

A total of 311 (35.5%) patients with HR+/HER2- ABC required a palbociclib dose reduction (93.6% due to AEs) from 125 to 100 mg. Mean patient age was 59.9 years, and 46.9% of patients had visceral disease. Median time to dose reduction was 70 days. The majority of dose reductions occurred within 3 months of starting palbociclib treatment. Incidences of all-grade and grades 3/4 hematologic AEs were lower following dose reduction.

CONCLUSIONS

A decrease in frequency and severity of hematologic AEs, including febrile neutropenia, following palbociclib dose reduction was observed, supporting the recommended use of dose reduction in AE management.

TRIAL REGISTRATION

These studies were sponsored by Pfizer. ClinicalTrials.gov: NCT00721409; registration date July 24, 2008. ClinicalTrials.gov: NCT01740427; registration date December 4, 2012. ClinicalTrials.gov: NCT01942135; registration date September 13, 2013.

Endocrine therapy for hormone receptor-positive, HER2-negative metastatic breast cancer: extending endocrine sensitivity

Targeted agents have significantly prolonged survival and improved response rates in first- and second-line settings of hormone receptor-positive/HER2-negative metastatic breast cancer. Optimal sequencing of the available options may prolong endocrine sensitivity, slow disease progression and delay the need for chemotherapy. However, the optimal treatment sequence remains unclear and therapeutic decisions are complex. We review the latest recommendations and supporting evidence for endocrine therapy in women with hormone receptor-positive/HER2-negative metastatic breast cancer and discuss strategies for the optimal sequential therapy in scenarios of response to endocrine therapy. Although more data are needed to define the best sequence of endocrine treatments, more personalized sequential strategies, which take into account response to previous treatments as well as disease symptoms and safety issues, will be increasingly feasible.

Treatment of Advanced Hormone Receptor-Positive (HR+) HER2-negative Breast Cancer

The article gives an overview of current treatment options for metastatic hormone receptor-positive and HER2-negative breast cancer. The focus is on combined therapies, e.g., with CDK4/6 inhibition compared with purely endocrine-based therapies in the pre- and postmenopause, presenting the latest study results. The addition of a CDK4/6 inhibitor to endocrine-based therapy with an aromatase inhibitor or fulvestrant leads to a marked improvement in progression-free survival and is independently beneficial whether palbociclib, ribociclib or abemaciclib is involved. The particular clinical status of inhibition of cyclin-dependent kinases argues for its use in the first-line treatment of women with metastatic, hormone receptor-positive and HER2-negative breast cancer compared with the available purely endocrine-based therapies.