CDK4/6 Inhibitor Treatments in Patients with Hormone Receptor Positive, Her2 Negative Advanced Breast Cancer: Potential Molecular Mechanisms, Clinical Implications and Future Perspectives

Landscape of Baseline and Acquired Genomic Alterations in Circulating Tumor DNA with Abemaciclib Alone or with Endocrine Therapy in Advanced Breast Cancer

PURPOSE

To identify potential predictors of response and resistance mechanisms in patients with hormone receptor-positive (HR+), HER2-negative (HER2-) advanced breast cancer (ABC) treated with the cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitor abemaciclib ± endocrine therapy (ET), baseline and acquired genomic alterations in circulating tumor DNA (ctDNA) were analyzed and associated with clinical outcomes.

EXPERIMENTAL DESIGN

MONARCH 3: postmenopausal women with HR+, HER2- ABC and no prior systemic therapy in the advanced setting were randomly assigned to abemaciclib or placebo plus nonsteroidal aromatase inhibitor (NSAI). nextMONARCH: women with HR+, HER2- metastatic breast cancer that progressed on/after prior ET and chemotherapy were randomly assigned to abemaciclib alone (two doses) or plus tamoxifen. Baseline and end-of-treatment plasma samples from patients in MONARCH 3 and nextMONARCH (monotherapy arms) were analyzed to identify somatic genomic alterations. Association between genomic alterations and median progression-free survival (mPFS) was assessed.

RESULTS

Most patients had ≥1 genomic alteration detected in baseline ctDNA. In MONARCH 3, abemaciclib+NSAI was associated with improved mPFS versus placebo+NSAI, regardless of baseline alterations. ESR1 alterations were less frequently acquired in the abemaciclib+NSAI arm than placebo+NSAI. Acquired alterations potentially associated with resistance to abemaciclib ± NSAI included RB1 and MYC.

CONCLUSIONS

In MONARCH 3, certain baseline ctDNA genomic alterations were prognostic for ET but not predictive of abemaciclib response. Further studies are warranted to assess whether ctDNA alterations acquired during abemaciclib treatment differ from other CDK4/6 inhibitors. Findings are hypothesis generating; further exploration is warranted into mechanisms of resistance to abemaciclib and ET. See related commentary by Wander and Bardia, p. 2008.

Preventing alpelisib-related hyperglycaemia in HR+/HER2-/PIK3CA-mutated advanced breast cancer using metformin (METALLICA): a multicentre, open-label, single-arm, phase 2 trial

Background

Hyperglycaemia is an early and frequent adverse event during alpelisib treatment. METALLICA aimed to evaluate prophylactic metformin to prevent or reduce hyperglycaemia occurrence in patients with HR+/HER2-/PIK3CA-mutated advanced breast cancer (ABC).

Methods

Between August 13th, 2020 and March 23rd, 2022, this 2-cohort, phase 2, multicentre, single-arm trial (NCT04300790) enrolled patients with HR+/HER2-/PIK3CA-mutated ABC: cohort A, normal glycaemia (fasting plasma glucose <100 mg/dL [<5.6 mmol/L] and HbA1c <5.7%), and cohort B, prediabetes (fasting plasma glucose 100-140 mg/dL [5.6-7.8 mmol/L] and/or haemoglobin A1C [HbA1c] 5.7-6.4%). Participants were at least 18 years old, with Eastern Cooperative Oncology Group performance status of 0-1, and up to two prior lines of endocrine therapy (ET) for ABC. Alpelisib plus ET were administered in 28-day cycles after initiation of prophylactic metformin plus ET. Primary endpoint was the incidence of grade 3-4 hyperglycaemia over the first 8 weeks. Secondary endpoints included safety, progression-free survival (PFS), objective response rate (ORR), and clinical benefit rate (CBR). The primary objective for cohort A and B is met with ≤7 (14.6%) and ≤4 (20%) patients with grade 3-4 hyperglycaemia over the first 8 weeks, respectively.

Findings

233 patients were screened, and 68 (20.2%) patients were enrolled in cohorts A (n = 48) and B (n = 20). Median follow-up was 7.8 months (IQR 1.4-19.6). Over the first 8 weeks, one (2.1%) of 48 patients in cohort A (95% CI: 0.5-11.1; P < 0.0001), and three (15.0%) of 20 patients in cohort B (95% CI: 5.6-37.8; P = 0.016) had grade 3-4 hyperglycaemia. Serious treatment-related adverse events occurred in seven patients (10.3%). The most common were rash (two [2.9%]), vomiting (two [2.9%]), and diarrhoea (two [2.9%]). Discontinuation of alpelisib caused by AEs was reported in nine patients (13.2%), none caused by hyperglycaemia. At data cutoff (15 June, 2022), no treatment-related deaths were observed. In the full analysis set, median PFS was 7.3 months (95% CI: 5.9-not reached), ORR was 20.6% (95% CI: 11.7-32.1%), and CBR was 52.9% (95% CI: 40.4-65.2).

Interpretation

In HR+/HER2-/PIK3CA-mutated ABC, prophylactic metformin before alpelisib plus endocrine treatment has low incidence and severity of alpelicib-induced hyperglycaemia.

Funding

Novartis Pharmaceuticals.

Efficacy of CDK4/6 inhibitors combined with endocrine therapy in HR+/HER2- breast cancer: an umbrella review

BACKGROUND

The use of Cyclin-Dependent kinase 4 and 6 (CDK4/6) inhibitors has profoundly changed the challenge of endocrine therapy (ET) resistance in hormone receptor-positive (HR+)/HER2-negative (HER2-) breast cancer. However, there is currently no comprehensive evaluation of the evidence for the efficacy of CDK4/6 inhibitors. We conducted an umbrella review to explore the impact of CDK4/6 inhibitor combined with ET on breast cancer by summarizing and assessing the meta-analysis (MA) and systematic review (SR) evidence.

METHODS

Cochrane, PubMed, Embase, and Web of Science databases were searched from inception to August 1st, 2022. Eligible studies were assessed for methodological quality, report quality, and evidence quality using the AMSTAR-2 scale, PRISMA 2020, and GRADE grading systems, respectively. We summarized all efficacy outcomes of CDK4/6 inhibitors for breast cancer and reported them in narrative form.

RESULTS

Our study included 24 MAs and SRs. The strongest evidence demonstrated that CDK4/6 inhibitor combined with ET significantly improved progression-free survival (PFS), overall survival (OS) in advanced breast cancer (ABC). A large body of moderate to high evidence showed a significant association between combination therapy and objective response rate (ORR), and clinical benefit response (CBR) benefit in ABC. Low evidence suggested some degree of benefit from combination therapy in second progression-free survival (PFS2) and time to subsequent chemotherapy (TTC) outcomes in ABC and invasive disease-free survival (IDFS) outcomes in early breast cancer.

CONCLUSIONS

Based on current evidence, CDK4/6 inhibitors combined with ET have great confidence in improving PFS, OS, ORR, and CBR outcomes in patients with ABC, which provides more rational and valid evidence-based medicine for CDK4/6 inhibitor promotion and clinical decision support.

Lipid changes during endocrine therapy in early-stage breast cancer patients: A real-world study

BACKGROUND

Endocrine drugs may affect lipid metabolism in breast cancer (BC) patients. This study explores lipid changes in early-stage BC patients taking different endocrine drugs.

METHODS

The changing trend of blood lipid during endocrine therapy in 2756 BC patients from January 2013 to December 2021 was retrospectively analyzed. The changes in four lipid parameters were assessed by the Generalized Linear Mixed Model, including total cholesterol (TC), triglycerides (TG), low-density lipoprotein (LDL-C), and high-density lipoprotein (HDL-C). These parameters were quantified at baseline and at 6, 12, 18, 24, 36, 48, 60, and 72 months after endocrine therapy initiation. Furthermore, a subgroup analysis according to menopausal status or medication types was conducted.

RESULTS

A total of 1201 patients taking aromatase inhibitors (AIs), including anastrozole (ANA), letrozole (LET), or exemestane (EXE), and 1555 patients taking toremifene (TOR) were enrolled. TC and TG levels showed a significantly elevated trend during 5 years of treatment (P < 0.05). HDL-C levels increased from baseline in the TOR group (P < 0.05). Compared with the postmenopausal AI group, the increasing trends of TC, TG, and LDL-C in the premenopausal AI group were more evident with the extension of time (β = 0.105, 0.027, 0.086, respectively). Within 3 years, TC, TG, and LDL-C levels in the ANA and LET groups were significantly higher than baseline (P < 0.05). Moreover, the levels of TG in the EXE group were significantly lower than that in the ANA or LET group (P < 0.05), but this significant difference disappeared after 3 years.

CONCLUSIONS

AIs significantly influenced lipid profiles more than TOR. AIs had a greater effect on blood lipids in premenopausal patients. Steroidal AIs (EXE) may affect lipid levels less than nonsteroidal AIs (ANA and LET).

Breast cancer and its therapeutic targets: A comprehensive review

Breast cancer is a common and deadly disease, so there is a constant need for research to find efficient targets and therapeutic approaches. Breast cancer can be classified on a molecular and histological base. Breast cancer can be divided into ER (estrogen receptor)-positive and ER-negative, HER2 (human epidermal growth factor receptor2)-positive and HER2-negative subtypes based on the presence of specific biomarkers. Targeting hormone receptors, such as the HER2, progesterone receptor (PR), and ER, is very significant and plays a vital role in the onset and progression of breast cancer. Endocrine treatments and HER2-targeted drugs are examples of targeted therapies now being used against these receptors. Emerging immune-based medicines with promising outcomes in the treatment of breast cancer include immune checkpoint inhibitors, cancer vaccines, and adoptive T-cell therapy. It is also explored how immune cells and the tumor microenvironment affect breast cancer development and treatment response. The major biochemical pathways, signaling cascades, and DNA repair mechanisms that are involved in the development and progression of breast cancer, include the PI3K/AKT/mTOR system, the MAPK pathway, and others. These pathways are intended to be inhibited by a variety of targeted drugs, which are then delivered with the goal of restoring normal cellular function. This review aims to shed light on types of breast cancer with the summarization of different therapeutic approaches which can target different pathways for tailored medicines and better patient outcomes.

CDK4/6 signaling attenuates the effect of epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors in EGFR-mutant non-small cell lung cancer

Background

Epidermal growth factor receptor (EGFR) mutations, such as exon 19 deletion and exon 21 L858R, are driver oncogenes of non-small cell lung cancer (NSCLC), with EGFR tyrosine kinase inhibitors (TKIs) being effective against EGFR-mutant NSCLC. However, the efficacy of EGFR-TKIs is transient and eventually leads to acquired resistance. Herein, we focused on the significance of cell cycle factors as a mechanism to attenuate the effect of EGFR-TKIs in EGFR-mutant NSCLC before the emergence of acquired resistance.

Methods

Using several EGFR-mutant cell lines, we investigated the significance of cell cycle factors to attenuate the effect of EGFR-TKIs in EGFR-mutant NSCLC.

Results

In several EGFR-mutant cell lines, certain cancer cells continued to proliferate without EGFR signaling, and the cell cycle regulator retinoblastoma protein (RB) was not completely dephosphorylated. Further inhibition of phosphorylated RB with cyclin-dependent kinase (CDK) 4/6 inhibitors, combined with the EGFR-TKI osimertinib, enhanced G0/G1 cell cycle accumulation and growth inhibition of the EGFR-mutant NSCLC in both in vitro and in vivo models. Furthermore, residual RB phosphorylation without EGFR signaling was maintained by extracellular signal-regulated kinase (ERK) signaling, and the ERK inhibition pathway showed further RB dephosphorylation.

Conclusions

Our study demonstrated that the CDK4/6-RB signal axis, maintained by the MAPK pathway, attenuates the efficacy of EGFR-TKIs in EGFR-mutant NSCLC, and targeting CDK4/6 enhances this efficacy. Thus, combining CDK4/6 inhibitors and EGFR-TKI could be a novel treatment strategy for TKI-naïve EGFR-mutant NSCLC.

Abemaciclib Is Effective in Palbociclib-Resistant Hormone Receptor-Positive Metastatic Breast Cancers

Cyclin-dependent kinases 4/6 inhibitor (CDK4/6i) plus endocrine therapy (ET) is standard of care for patients with hormone receptor (HR)-positive, HER2-negative metastatic breast cancer (MBC). However, resistance to CDK4/6is plus ET remains a clinical problem with limited therapeutic options following disease progression. Different CDK4/6is might have distinct mechanisms of resistance, and therefore using them sequentially or targeting their differentially altered pathways could delay disease progression. To understand pathways leading to resistance to the CDK4/6is palbociclib and abemaciclib, we generated multiple in vitro models of palbociclib-resistant (PR) and abemaciclib-resistant (AR) cell lines as well as in vivo patient-derived xenografts (PDX) and ex vivo PDX-derived organoids (PDxO) from patients who progressed on CDK4/6i. PR and AR breast cancer cells exhibited distinct transcriptomic and proteomic profiles that sensitized them to different classes of inhibitors; PR cells upregulated G2-M pathways and responded to abemaciclib, while AR cells upregulated mediators of the oxidative phosphorylation pathway (OXPHOS) and responded to OXPHOS inhibitors. PDX and organoid models derived from patients with PR breast cancer remained responsive to abemaciclib. Resistance to palbociclib while maintaining sensitivity to abemaciclib was associated with pathway-specific transcriptional activity but was not associated with any individual genetic alterations. Finally, data from a cohort of 52 patients indicated that patients with HR-positive/HER2-negative MBC who progressed on palbociclib-containing regimens can exhibit a meaningful overall clinical benefit from abemaciclib-based therapy when administered after palbociclib. These findings provide the rationale for clinical trials evaluating the benefit of abemaciclib treatment following progression on a prior CDK4/6i.

SIGNIFICANCE

Palbociclib-resistant breast cancers respond to abemaciclib and express pathway-specific signatures of sensitivity, providing a biomarker-driven therapeutic option for patients with metastatic breast cancer following disease progression on cyclin-dependent kinases 4/6 inhibitors.

Disproportionality Analysis of Abemaciclib in the FDA Adverse Event Reporting System: A Real-World Post-Marketing Pharmacovigilance Assessment

BACKGROUND AND OBJECTIVE

Abemaciclib, a cyclin-dependent kinase 4 and 6 inhibitor, demonstrated efficacy in women with hormone receptor-positive, human epidermal growth factor receptor 2-negative advanced breast cancer. Because of the limitations of clinical trials, which are not representative of large real-world populations, rare events and long-term safety concerns cannot be detected. The current study aimed to evaluate the adverse events of abemaciclib through data mining of the Food and Drug Administration Adverse Event Reporting System (FAERS).

METHODS

Reporting odds ratio and Bayesian confidence propagation neural network of information components were used to quantify the adverse event signals of abemaciclib from the third quarter of 2017 to the first quarter of 2022. Serious and non-serious cases were compared using the Mann-Whitney U test or Chi-squared test, and clinical priority was assigned to signals by scoring (range 0-10 points) five features using a rating scale.

RESULTS

A total of 6125 reports of abemaciclib as the "primary suspected" and 72 significant adverse events of abemaciclib were identified. Common adverse events, such as diarrhea, neutropenia, alanine transaminase, aspartate transaminase, and serum creatinine increases, and other adverse events, including thrombosis, deep vein thrombosis, pulmonary embolism, interstitial lung disease, and pneumonitis were of high concern. Of note, 17 preferred terms were classified as unexpected adverse events that uncovered in the label. In addition, 1, 26, and 45 adverse events were identified as strong, moderate, and weak clinical priorities. The median time to onset for strong, moderate, and weak clinical priority signals was 49, 22, and 28 days, respectively. All of the disproportionality signals had early failure type features, suggesting that adverse events of abemaciclib gradually decreased over time.

CONCLUSIONS

The discovery of disproportionality signals could potentially prompt improved awareness of toxicities for abemaciclib, and the results of time to onset, serious and non-serious reports, and clinical priority analyses provided some supporting evidence for clinicians to manage adverse events.

Prognostic value of [18F]-FDG PET/CT in patients with meta-static breast cancer treated with cyclin-dependent inhibitors

Objective

The addition of cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) to endocrine therapy impressively improved the outcome of patients with hormone receptor-positive metastatic breast cancer. Despite their great efficacy, not all patients respond to treatment and many of them develop acquired resistance. The aim of this retrospective study was to assess the role of [18F]-FDG PET/CT in predicting PFS and OS in breast cancer patients treated with CDK4/6i.

Methods

114 patients who performed an [18F]-FDG PET/CT scan before (PET1) and 2-6 months (PET2) after starting treatment were retrospectively enrolled. Metabolic response was evaluated by EORTC, PERCIST and Deauville Score and correlated to PFS and OS.

Results

In patients who did not progress at PET2 (n = 90), PFS rates were not significantly different between classes of response by EORTC and PERCIST. Conversely, patients showing a Deauville score ≤3 had a longer PFS (median PFS 42 vs 21.0 months; p = 0.008). A higher total metabolic tumor volume at PET1 (TMTV1) was also associated with a shorter PFS (median 18 vs 42 months; p = 0.0026). TMTV1 and Deauville score were the only independent prognostic factors for PFS at multivariate analysis and their combination stratified the population in four definite classes of relapse risk. Conversely, the above parameters did not affect OS which was only influenced by a progressive metabolic disease at PET2 (3-years survival rate 29.8 vs 84.9%; p<0.0001).

Conclusion

TMTV and metabolic response by Deauville score were significant prognostic factors for PFS in patients with breast cancer treated with CDK4/6i. Their determination could help physicians to select patients who may need a closer follow up.

Cannabidiol as a Promising Adjuvant Therapy for Estrogen Receptor-Positive Breast Tumors: Unveiling Its Benefits with Aromatase Inhibitors

BACKGROUND

Estrogen receptor-positive (ER⁺) breast cancer is the most diagnosed subtype, with aromatase inhibitors (AIs) being one of the therapeutic drug types used in the clinic. However, endocrine resistance may develop after prolonged treatment, and different approaches, such as combining endocrine and targeted therapies, have been applied. Recently, we demonstrated that cannabidiol (CBD) induces anti-tumor actions in ER⁺ breast cancer cells by targeting aromatase and ERs. Considering this, we studied, in vitro, whether CBD when combined with AIs could improve their effectiveness.

METHODS

MCF-7aro cells were used and the effects on cell viability and on the modulation of specific targets were investigated.

RESULTS

CBD when combined with anastrozole (Ana) and letrozole (Let) caused no beneficial effect in comparison to the isolated AIs. In contrast, when combined with the AI exemestane (Exe), CBD potentiated its pro-cell death effects, abolished its estrogen-like effect, impaired ERα activation, and prevented its oncogenic role on the androgen receptor (AR). Moreover, this combination inhibited ERK_1/2 activation, promoting apoptosis. The study of the hormonal microenvironment suggests that this combination should not be applied in early stages of ER⁺ breast tumors.

CONCLUSIONS

Contrary to Ana and Let, this study highlights the potential benefits of combining CBD with Exe to improve breast cancer treatment and opens up the possibility of new therapeutic approaches comprising the use of cannabinoids.

Down-regulation of RB1 and miR-132 in ductal carcinoma of the breast

INTRODUCTION

miR-132-3p acts in normal breast development and its downregulation has been documented in breast cancer. One of the targets of miR-132-3p is RB1 which is also inactivated in breast cancer. The interactions between RB1 and miR-132 have been reported in several pathological conditions. We aimed to investigate the correlation between expression levels of miR-132 and RB1 in ductal carcinoma of the breast.

METHODS

The study was carried out on tissues obtained from female patients with primary breast cancer. Tumor samples were classified using clinical and pathological data. Following RNA extraction and cDNA synthesis, relative gene expressions in tumors were compared to non-cancerous adjacent tissues. The link between RB1 and miR-132 was assessed by the correlation coefficient test.

RESULTS

Our findings revealed a significant decrease in miR-132 and RB1 expressions with a ratio of 0.165 and 0.365, respectively. Tumor grade showed an association with miRNA-132 levels. The expression of miR-132 in grade I tumors was almost equal to that of normal adjacent tissues, but was intensely decreased in grades II and III. The correlation analysis showed a small linear association between RB1 and miR-132 levels.

CONCLUSION

The reduction of miR-132 and RB1 expression confirmed the tumor-suppressive role of both genes in breast cancer. Considering that RB1 is one of the miR-132 targets, further studies are required to discover any miRNA-mediated upregulation role for miR-132. Our finding discovered a small linear association between miR-132 and RB1, which can be concluded towards their independent function in breast cancer pathogenesis.

Integration of multi-omics data reveals a novel hybrid breast cancer subtype and its biomarkers

Tumor heterogeneity in breast cancer hinders proper diagnosis and treatment, and the identification of molecular subtypes may help enhance the understanding of its heterogeneity. Therefore, we proposed a novel integrated multi-omics approach for breast cancer typing, which led to the identification of a hybrid subtype (Mix_Sub subtype) with a poor survival prognosis. This subtype is characterized by lower levels of the inflammatory response, lower tumor malignancy, lower immune cell infiltration, and higher T-cell dysfunction. Moreover, we found that cell-cell communication mediated by NCAM1-FGFR1 ligand-receptor interaction and cellular functional states, such as cell cycle, DNA damage, and DNA repair, were significantly altered and upregulated in patients with this subtype, and that such patients displayed greater sensitivity to targeted therapies. Subsequently, using differential genes among subtypes as biomarkers, we constructed prognostic risk models and subtype classifiers for the Mix_Sub subtype and validated their generalization ability in external datasets obtained from the GEO database, indicating their potential therapeutic and prognostic significance. These biomarkers also showed significant spatially variable expression in malignant tumor cells. Collectively, the identification of the Mix_Sub breast cancer subtype and its biomarkers, based on the driving relationship between omics, has deepened our understanding of breast cancer heterogeneity and facilitated the development of breast cancer precision therapy.

Functional and Phenotypic Characterisations of Common Syngeneic Tumour Cell Lines as Estrogen Receptor-Positive Breast Cancer Models

Estrogen receptor-positive breast cancers (ER+ BCas) are the most common form of BCa and are increasing in incidence, largely due to changes in reproductive practices in recent decades. Tamoxifen is prescribed as a component of standard-of-care endocrine therapy for the treatment and prevention of ER+ BCa. However, it is poorly tolerated, leading to low uptake of the drug in the preventative setting. Alternative therapies and preventatives for ER+ BCa are needed but development is hampered due to a paucity of syngeneic ER+ preclinical mouse models that allow pre-clinical experimentation in immunocompetent mice. Two ER-positive models, J110 and SSM3, have been reported in addition to other tumour models occasionally shown to express ER (for example 4T1.2, 67NR, EO771, D2.0R and D2A1). Here, we have assessed ER expression and protein levels in seven mouse mammary tumour cell lines and their corresponding tumours, in addition to their cellular composition, tamoxifen sensitivity and molecular phenotype. By immunohistochemical assessment, SSM3 and, to a lesser extent, 67NR cells are ER+. Using flow cytometry and transcript expression we show that SSM3 cells are luminal in nature, whilst D2.0R and J110 cells are stromal/basal. The remainder are also stromal/basal in nature; displaying a stromal or basal Epcam/CD49f FACS phenotype and stromal and basal gene expression signatures are overrepresented in their transcript profile. Consistent with a luminal identity for SSM3 cells, they also show sensitivity to tamoxifen in vitro and in vivo. In conclusion, the data indicate that the SSM3 syngeneic cell line is the only definitively ER+ mouse mammary tumour cell line widely available for pre-clinical research.

Position paper on CDK4/6 inhibitors in early breast cancer

Inhibitors of the cyclin-dependent kinases 4/6 (CDK4/6i) have been practice-changing and are now considered the standard of care in combination with endocrine therapy for the first- or second-line treatment in advanced hormone-receptor-positive, human epidermal growth factor receptor 2‑negative breast cancer. Recently, CDK4/6i have also emerged as an appealing targeted cancer therapy in early breast cancer, however results of large clinical trials are controversial. This position paper summarizes the evidence, and provides guidance for clinical practice.

CDK4/6 Inhibitors Overcome Endocrine ESR1 Mutation-Related Resistance in Metastatic Breast Cancer Patients

ESR1 mutations contribute to endocrine resistance and occur in a high percentage of hormone-receptor-positive (HR+) metastatic breast cancer (mBC) cases. Cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) changed the treatment landscape of HR+ mBC, as they are able to overcome estrogen resistance. The present retrospective study investigates the clinical benefit of CDK4/6i in ESR1 mutant HR+ mBC patients treated with a CDK4/6i as first- or second-line therapy. Plasma was collected at baseline prior to CDK4/6i plus hormone therapy as a first- or second-line treatment. Circulating free DNA (cfDNA) was extracted from plasma, and ESR1 mutation analysis was performed on a ddPCR. Statistical analyses were performed to investigate the predictive power of ESR1 mutations and any association with clinical factors. A total of 42 patients with mBC treated with CDK4/6i plus endocrine therapy as first- (n = 35) or second-line (n = 7) were enrolled. Twenty-eight patients received hormonal therapy (AI or tamoxifen) in the adjuvant setting. ESR1 mutation status in blood was associated with shorter median disease-free survival (DFS) (30 vs. 110 months; p = 0.006). Multivariate analysis confirmed ESR1 mutations as independent factors of resistance in adjuvant hormone therapy. On the contrary, no difference in progression-free survival (PFS) was observed in the presence or absence of an ESR1 mutation in patients treated with CDK4/6i as first-line treatment (p = 0.29). No statistically significant correlation between the best response to CDK4/6i and ESR1 mutation was found (p = 0.46). This study indicates that the ESR1 mutation detected in cfDNA is an independent predictive factor of clinical recurrence in the adjuvant setting and that CDK4/6i can overcome ESR1-dependent resistance.

CDK4/6 Inhibitors in Advanced HR+/HER2 - Breast Cancer: A Multicenter Real-World Data Analysis

Purpose

CDK4/6 inhibitors (CDK4/6i) combined with endocrine therapy are considered standard-of-care for first-line therapy of patients with hormone receptor positive, HER2 negative, advanced breast cancer (HR+/HER2- ABC). Superiority of combination therapy over endocrine monotherapy has been demonstrated in a multitude of randomized controlled trials (RCTs) in phase III and IV. However, RCTs reflect clinical reality only to a limited extent, as narrow inclusion criteria lead to a selected patient collective. Here, we present real-world data (RWD) on CDK4/6i treatment in patients with HR+/HER2- ABC at four certified German university breast cancer centers.

Methods

Patients diagnosed with HR+/HER2- ABC who were treated in clinical routine with CDK4/6i between November 2016 and December 2020 at four certified German university breast cancer centers (Saarland University Medical Center, University Medical Center Charité Berlin, University Medical Center Bonn, and University Medical Center Hospital Schleswig-Holstein, Campus Kiel) were identified and enrolled in this retrospective study. Clinicopathological characteristics and clinical outcomes were recorded with particular emphasis on CDK4/6i therapy course [progression-free survival (PFS) following treatment initiation, toxicity, dose reduction, therapy discontinuation, prior and subsequent therapy line].

Results

Data from n = 448 patients were evaluated. The mean patient age was 63 (±12) years. Of these patients, n = 165 (36.8%) were primarily metastasized, and n = 283 (63.2%) had secondary metastatic disease. N = 319 patients (71.3%) received palbociclib, n = 114 patients (25.4%) received ribociclib, and n = 15 patients (3.3%) received abemaciclib, respectively. Dose reduction was performed in n = 132 cases (29.5%). N = 57 patients (12.7%) discontinued the treatment with CDK4/6i due to side effects. N = 196 patients (43.8%) experienced disease progression under CDK4/6i treatment. The median PFS was 17 months. Presence of hepatic metastases and prior therapy lines were associated with shorter PFS, whereas estrogen positivity and dose reduction due to toxicity were positively associated with PFS. Presence of bone and lung metastases, progesterone positivity, Ki67 index, grading, BRCA1/2 and PIK3CA mutation status, adjuvant endocrine resistance, and age did not significantly impact on PFS.

Conclusion

Our RWD analysis on CDK4/6i treatment in Germany supports data from RCTs regarding both treatment efficacy and safety of CDK4/6i for treatment of patients with HR+/HER2- ABC. In comparison to data from the pivotal RCTs, median PFS was lower but within the expected range for RWD, which could result from inclusion of patients with more advanced diseases (i.e., higher therapy lines) to our dataset.

Comparison of changes in lipid profiles of premenopausal women with early-stage breast cancer treated with different endocrine therapies

Adjuvant endocrine therapy improves the prognosis of early breast cancer with hormone receptor positivity. However, there is no systematic report on the effect of endocrine therapy (particularly ovarian function suppression, OFS) on serum lipids in premenopausal women. This retrospective cohort study aimed to determine whether various endocrine treatments had different effects on blood lipids. This study enrolled 160 premenopausal patients with stage I-III breast cancer in eastern China. The initial diagnostic information was retrieved from patient's medical records, including age at the time of diagnosis, tumor characteristics, anticancer treatment and past medical history. The changes in blood lipids in patients receiving different types of endocrine therapy were compared at the 3rd, 6th, 12th, and 24th months after initiating endocrine therapy. Generalized linear mixed model was used in our analyses. Our data revealed that low-density lipoprotein cholesterol (LDL-C) levels in patients with tamoxifen (TAM) were significantly lower in the 6th, 12th, and 24th months than that in the 3rd month, while high-density lipoprotein cholesterol (HDL-C) levels in the 6th, 12th, and 24th months were significantly higher than that in the 3rd month, indicating that blood lipid levels generally improved with time. While in TAM plus OFS group, HDL-C levels were significantly higher in the 24th month than in the 3rd month, total cholesterol (TC) levels were significantly higher in the 24th month than in the 6th month. The lipid profiles of OFS plus aromatase inhibitor (AI) group did not show significant differences at any time point but were significantly higher than those of the other two groups especially in LDL and TC. TAM group tended to have lower serum lipid levels. With longer follow-up, no statistically significant difference in values was observed between TAM and TAM plus OFS groups at various time points. Compared with the other two groups, OFS plus AI group presented an increasing trend toward LDL-C and TC. The risk of dyslipidemia requires further investigation using a large sample size.

Budget impact analysis of breast cancer medications: a systematic review

BACKGROUND

Breast cancer (BC) is the most common cancer globally among women, with 2,261,419 new cases in 2020; systemic treatment may be neo-adjuvant, adjuvant, or both. BC subtype guides the standard systemic therapy administered, which consists of endocrine therapy for all HR + tumors, trastuzumab-based HER2-directed antibody therapy plus chemotherapy for all HER2 + tumors (with endocrine therapy given in addition, if concurrent HR positivity), and chemotherapy alone for the triple-negative subtype. This study aimed to identify, evaluate, and systematically review all budget impact analyses (BIAs) of BC medications worldwide.

METHODS

PubMed, Scopus, and Web of Science Core Collection databases were thoroughly searched up to 26th March 2022 to identify original published studies which evaluate BIA of BC medications. ISPOR Task Force guidelines were used to assess the quality of included studies. This study was conducted and reported following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines.

RESULTS

In total, 17 BIAs were included in the study. About half of the studies were conducted in Europe. The results of the BIAs showed that most of the included BIAs are conducted from the payer's perspective; they have different methodological frameworks for recommended chemotherapy, targeted therapy, and immunotherapy agents to treat BC. For the same medications, the results of budgetary effects are not consistent in diverse countries. Nine out of the 17 studies were focused on trastuzumab, in which the biosimilar form reduced costs, but the brand form increased costs, especially in a 52-week treatment period.

CONCLUSION

Researchers should conduct the budget impact analysis of high-value medications such as anti-tumor drugs more objectively, and the accuracy of parameters needs to be more strictly guaranteed. Furthermore, it is worthy of declaring that the budgetary impact of the same drug is not always consistent over time, so the researchers should measure access to medication in the long run.

Facing the CDK4/6i resistance dilemma in patients with breast cancer, exploration of the resistance mechanism and possible reverse strategy: A narrative review

Breast cancer is one of the highest rates of malignancy of women, approximate 70% metastatic breast cancer are hormone receptor positive (HR+) and human epidermal growth factor receptor 2 negative (HER2-). Hormone therapy is the primary strategy of HR+/HER2- metastatic breast cancer. With the permission of cyclin-dependent kinase 4 and 6 inhibitors (CDK4/6i), progress free survival and overall survival were significantly licensed. However, inevitable outcome of CDK4/6i resistance has become the main reason that restricts the clinical benefit of patients. In recent years, the research on dealing with drug resistance has become a hot topic, a large number of molecular mechanisms have been focused, and a lot of experiments have been carried out at the preclinical level. This review summarizes the current knowledge of CDK4/6i resistance mechanism, systematically expounds the signaling pathways and targets leading to CDK4/6i resistance, analyzes different ways and mechanisms, and provides theoretical guidance for the clinical reversal of endocrine therapy resistance.

Clinical management of metastatic hormone receptor-positive, HER2-negative breast cancer (MBC) after CDK 4/6 inhibitors: a retrospective single-institution study

PURPOSE

Cyclin-dependent kinase 4/6 inhibitors (CDK4/6is), in combination with endocrine therapy (ET), are standard either in the first (1L) or second-line (2L) setting for the treatment of hormone receptor (HR) positive, HER2-negative metastatic breast cancer (MBC). However, the optimal sequencing of treatments after progression on CDK4/6i remains unknown. We performed a single-institution analysis to identify treatments and outcomes after progression on a CDK4/6i.

METHODS

We identified patients with HR-positive, HER2-negative MBC prescribed a CDK4/6i in the 1L or 2L settings from December 2014 to February 2018 at Mayo Clinic in Rochester, Minnesota. Outcomes were collected through September 30, 2020.

RESULTS

Palbociclib, in combination with letrozole or fulvestrant, was the most prescribed CDK4/6i. The 1L and 2L CDK4/6i cohorts exhibited comparable overall survival (OS), but progression-free survival (PFS) was longer in the 1L than the 2L cohort [28.2 months (95% CI 19.6-34.9) vs 19.8 months (95% CI 15.7-29.6)]. The most common post-CDK4/6i treatments were PI3K/mTOR inhibitors (PI3K/mTORi), single-agent ET, or chemotherapy. PFS in the 1L CDK4/6i cohort following PI3K/mTORi was 8.5 months (95% CI 5.5 months-NE), single-agent ET was 6.0 months (95% CI 3.3-14.0 months), and chemotherapy PFS was 5.4 months (95% CI 3.3 months-NE).

CONCLUSIONS

Following progression on a CDK 4/6i, mPFS was short, with similar PFS times comparing chemotherapy and ET, with slightly longer PFS for targeted strategies (PI3K/mTOR). These results highlight a major need to better understand the mechanisms of CDK4/6i resistance and identify new therapeutic strategies for these patients.

The Combination of CDK 4/6 Inhibitors plus Endocrine Treatment versus Endocrine Treatment Alone in Hormone-receptor (HR)-Positive breast Cancer: a Systematic Review and Meta-analysis

Background

The identification of the novel targeted therapy i.e., cyclin-dependent kinases (CDKs) 4/6 inhibitor as combined with the endocrine regimen revealed a considerable capability to increase the managements' effectivity of hormone-receptor-positive (HR+) and HER2- breast cancer (BC).

Objective

This study aims to compare the latter combination strategies versus hormonal therapy alone to determine its applicability in the treatment of HR+/HER2- BC.

Methods

We established the review based on the clinical trials as collected from several scientific databases from January 2011 to April 2021. RevMan 5.4 was utilized in statistical analysis and risk of bias (RoB) measurement. 5110 participants from 9 different trials were included in this review with similar baseline characteristics.

Results

According to our analysis of the intention-to-treat (ITT) group, CDK 4/6 inhibitor arms exhibited better overall response rate (ORR) as indicated by the relative risk (RR) (randomized-effect model (REM), 1.59 [1.37, 1.86]; 95% confidence interval (CI); P <0.00001) and higher clinical benefit rate (CBR) (RR, 1.22 [1.13, 1.32]; 95% CI; REM; P <0.00001). The combination regiment also proved to be effective in reducing the rate of progressive disease (PD) in the ITT group (RR 0.46 [0.39, 0.54]; CI 95%; FEM; P <0.00001. Although the rate of adverse effects especially the hematological reactions was significantly lower in the endocrine alone arm, other system reactions were fairly comparable.

Conclusion

The introduction of CDK 4/6 inhibitor to the endocrine-based regiment is proved beneficial to patients with HR+/HER2- BC even though the most recommended anti-hormonal to be combined remains questionable.

The role of HER2 alterations in clinicopathological and molecular characteristics of breast cancer and HER2-targeted therapies: a comprehensive review

Breast cancer (BC) is the most common malignancy in women and one of the leading causes of cancer mortality, despite significant treatment advancements over the last decades. Human epidermal growth factor receptor-2 (HER2) is a member of the ERBB family of receptor tyrosine kinases which have long been known to mediate cancer cell growth and invasion through constitutive activation of oncogenic downstream signaling, such as PI3K/Akt/mTOR and MAPK. Overexpression/amplification of HER2 in various tumors, especially BC, offers the possible therapeutic potential for target therapies. HER2-targeted therapies, either with a combination of chemotherapy or through multi-anti-HER2 therapies without chemotherapy, have significantly improved the prognosis of HER2-positive tumors. In recent years, novel anti-HER2 agents and combination therapies have garnered much attention, especially for heavily treated advanced or metastatic BCs. HER2-positive BC is biologically a heterogeneous group depending on HER2 activation mechanisms, hormone receptor status, genome variations, tumor heterogeneity, and treatment resistance, which affect the treatment benefit and patients' outcomes. This review will discuss HER2 alternations (gene amplification or receptor overexpression) in BC, their correlation with clinicopathological characteristics and molecular characteristics, and HER2-based therapies in tumors with HER2 overexpression/amplification.

Efficacy of cyclin-dependent kinase 4/6 inhibitors in patients with metastatic hormone positive breast cancer: a single institutional study from India

PURPOSE

Cyclin-dependent kinase 4/6 (CDK4/6) inhibitors have shown marked benefit in the treatment of hormone positive metastatic breast cancer (HR+ MBC). There are limited real-world studies with palbociclib and ribociclib. Here we report our experience with CDK4/6 inhibitors in these groups of patients.

MATERIAL AND METHODS

Patients with HR+ MBC who have received either palbociclib or ribociclib during the course of their treatment from January 2017 to January 2022 were included in the study. The baseline demographic features, treatment details and toxicity were recorded. Patients who received at least 1 month of therapy were included in the survival analysis.

RESULTS

A total of 144 patients received CDK4/6 inhibitors during the time period. The median age of the population was 53 (30-80) years. Ninety-eight (71.4%) patients presented with de novo metastatic disease. The most common site of metastasis was to the skeleton (74.2%). Most patients (75%) received palbociclib as their therapy. At a median follow-up of 20.2 months, the median progression free survival (PFS) of the whole population was 16.5 (95% confidence interval (95% CI): 11.6-25.5) months and the median overall survival (OS) was 29.7 (95% CI: 21.7-44.6) months. The presence of liver metastases, low progesterone receptor positivity (Allred score < 6) and prior systemic treatment were poor prognostic factors for both PFS and OS in multivariate analysis. Drug was discontinued for only 2.1% of the patient population.

CONCLUSIONS

Use of CDK4/6 inhibitors has led to improvement in PFS and OS in patients with HR+ MBC and it is well tolerated. The presence of liver metastases and low progesterone receptor positivity (Allred score < 6) and prior treatment are poor prognostic factors.

Breast cancer in the era of precision medicine

Breast cancer is a heterogeneous disorder with different molecular subtypes and biological characteristics for which there are diverse therapeutic approaches and clinical outcomes specific to any molecular subtype. It is a global health concern due to a lack of efficient therapy regimens that might be used for all disease subtypes. Therefore, treatment customization for each patient depending on molecular characteristics should be considered. Precision medicine for breast cancer is an approach to diagnosis, treatment, and prevention of the disease that takes into consideration the patient's genetic makeup. Precision medicine provides the promise of highly individualized treatment, in which each individual breast cancer patient receives the most appropriate diagnostics and targeted therapies based on the genetic profile of cancer. The knowledge about the molecular features and development of breast cancer treatment approaches has increased, which led to the development of new targeted therapeutics. Tumor genomic profiling is the standard of care for breast cancer that could contribute to taking steps to better management of malignancies. It holds great promise for accurate prognostication, prediction of response to common systemic therapies, and individualized monitoring of the disease. The emergence of targeted treatment has significantly enhanced the survival of patients with breast cancer and contributed to reducing the economic costs of the health system. In this review, we summarized the therapeutic approaches associated with the molecular classification of breast cancer to help the best treatment selection specific to the target patient.

Immune effects of CDK4/6 inhibitors in patients with HR+/HER2− metastatic breast cancer: Relief from immunosuppression is associated with clinical response

Background

Cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) are innovative small target molecules that, in combination with endocrine therapy, have recently been employed in the treatment of patients with HR⁺/HER2⁻ metastatic breast cancer (mBC). In this prospective study, we investigate the impact of CDK4/6i on the immune profile of patients with HR⁺/HER2⁻ mBC.

Methods

Immune cell subsets were analysed using flow cytometry of peripheral blood mononuclear cells (PBMCs) isolated from patients with HR⁺/HER2⁻ mBC, both before and during treatment. Regulatory T cells (Tregs) were identified using the markers CD4, CD25, CTLA4, CD45RA, and intracellular FOXP3. Monocytic and polymorphonuclear myeloid-derived suppressor cells (M-MDSCs and PMN-MDSCs) and other immune populations were analysed using CD45, CD14, CD66b, CD11c, HLA-DR, CD3, CD8, CD28, CD137, PD1, CD45RA, CCR7, and Ki67.

Findings

The percentage of circulating Tregs and M/PMN-MDSCs was significantly downregulated from baseline during CDK4/6i-treatment (p<0.0001 and p<0.05, respectively). In particular, the effector Treg subset (CD4⁺CD25⁺FOXP3^highCD45RA⁻) was strongly reduced (p<0.0001). The decrease in Treg levels was significantly greater in responder patients than in non-responder patients. Conversely, CDK4/6i treatment was associated with increased levels of CD4⁺ T cells and anti-tumour CD137⁺CD8⁺ T cells (p<0.05).

Interpretation

CDK4/6i treatment results in downregulation of Tregs, M-MDSCs, and PMN-MDSCs, thus weakening tumour immunosuppression. This decrease is associated with response to treatment, highlighting the importance of unleashing immunity in cancer treatment efficacy. These results suggest a novel mechanism of immunomodulation in mBC and provide valuable information for the future design of novel treatments combining CDK4/6i with immunotherapy in other cancer settings.

Funding

Sapienza University of Rome.

Therapeutic potential of CDK4/6 inhibitors in renal cell carcinoma

The treatment of advanced and metastatic kidney cancer has entered a golden era with the addition of more therapeutic options, improved survival and new targeted therapies. Tyrosine kinase inhibitors, mammalian target of rapamycin (mTOR) inhibitors and immune checkpoint blockade have all been shown to be promising strategies in the treatment of renal cell carcinoma (RCC). However, little is known about the best therapeutic approach for individual patients with RCC and how to combat therapeutic resistance. Cancers, including RCC, rely on sustained replicative potential. The cyclin-dependent kinases CDK4 and CDK6 are involved in cell-cycle regulation with additional roles in metabolism, immunogenicity and antitumour immune response. Inhibitors of CDK4 and CDK6 are now commonly used as approved and investigative treatments in breast cancer, as well as several other tumours. Furthermore, CDK4/6 inhibitors have been shown to work synergistically with other kinase inhibitors, including mTOR inhibitors, as well as with immune checkpoint inhibitors in preclinical cancer models. The effect of CDK4/6 inhibitors in kidney cancer is relatively understudied compared with other cancers, but the preclinical studies available are promising. Collectively, growing evidence suggests that targeting CDK4 and CDK6 in kidney cancer, alone and in combination with current therapeutics including mTOR and immune checkpoint inhibitors, might have therapeutic benefit and should be further explored.

Safety in Japanese Advanced Breast Cancer Patients Who Received Abemaciclib in MONARCH 2 and MONARCH 3: Assessment of Treatment-Emergent Neutropenia, Diarrhea, and Increased Alanine Aminotransferase and Aspartate Aminotransferase Levels

Purpose

Our objective was to gain a better understanding of the safety of abemaciclib in Japanese patients with hormone receptor-positive, human epidermal growth factor receptor 2-negative advanced breast cancer.

Patients and Methods

Treatment-emergent adverse events (TEAEs) were assessed in pooled Japanese subpopulation data from two phase 3 studies assessing abemaciclib/placebo in combination with fulvestrant (MONARCH 2; M2) or non-steroidal aromatase inhibitors (MONARCH 3; M3). For common, clinically relevant TEAEs, event characteristics and management were summarized by study.

Results

In the Japanese safety subpopulation (abemaciclib: N=101; placebo: N=46), all patients experienced ≥1 TEAE (Grade ≥ 3: abemaciclib, 71.3%; placebo, 23.9%; no Grade 5). Clinically relevant TEAEs that were more frequent in abemaciclib-treated Japanese patients compared to the overall safety populations included diarrhea (any grade, 95.0%; Grade ≥ 3, 12.9%), neutropenia (any grade, 75.2%; Grade 3–4, 35.6%), increased alanine aminotransferase (ALT; any grade, 39.6%; Grade 3–4, 14.9%), and increased aspartate aminotransferase (AST; any grade, 37.6%; Grade 3–4, 8.9%). Diarrhea was Grade ≤3 and successfully managed with medications (≥87%) and dose reductions (≤25%) and/or omissions (≤23.3%). Most Grade ≥2 diarrhea occurred in the first treatment cycle, declining thereafter. Neutropenia, the most common Grade ≥3 TEAE in abemaciclib-treated Japanese patients, was generally manageable with dose omissions (M2: 42.0%; M3: 23.1%) and/or reductions (M2: 16%; M3: 15.4%). Neutrophil counts plateaued after Cycle 2, recovering to pretreatment levels after discontinuation of abemaciclib. Hepatic events were managed with medication (≤21%) and dose adjustments (≤33.3%), with most Grade ≥2 events occurring in early treatment cycles. Discontinuation of any study treatment in Japanese patients occurred more frequently due to increased ALT/AST (M2: 9.1%/10.5%; M3: 16.7%/10.5%) compared with diarrhea (M2: 0%; M3: 2.8%) or neutropenia (M2: 0%; M3: 3.8%).

Conclusion

Abemaciclib was well tolerated in Japanese patients in MONARCH 2 and MONARCH 3, with common, clinically relevant TEAEs manageable with appropriate interventions.

Clinical Significance of PIK3CA and ESR1 Mutations in circulating tumor DNA: Analysis from the MONARCH 2 Study of Abemaciclib Plus Fulvestrant

BACKGROUND

PIK3CA and ESR1 mutations have been implicated in resistance to endocrine therapy (ET) in HR+, HER2- advanced breast cancer (ABC). Inhibition of CDK4&6 has been hypothesized as a therapeutic strategy to overcome endocrine resistance in patients with PIK3CA- or ESR1-mutant breast cancers. The objective of this exploratory analysis was to assess efficacy of abemaciclib plus fulvestrant in patients with or without PIK3CA or ESR1 mutations in MONARCH 2.

PATIENTS AND METHODS

MONARCH 2 was a global, randomized, double-blind Phase 3 trial of abemaciclib plus fulvestrant in women with HR+, HER2- ABC that had progressed on ET. Patients were randomized 2:1 to receive abemaciclib plus fulvestrant or placebo plus fulvestrant. Exploratory analyses assessed progression-free survival (PFS) and overall survival (OS), and other endpoints, in patients with or without PIK3CA or ESR1 mutations detectable in baseline ctDNA.

RESULTS

Abemaciclib plus fulvestrant improved PFS compared to placebo plus fulvestrant in both PIK3CA-wild-type and PIK3CA-mutant subgroups, as well as both ESR1-wild-type and ESR1-mutant subgroups. Additional endpoints, including OS, were also improved following treatment with abemaciclib plus fulvestrant regardless of PIK3CA or ESR1 mutation status.

CONCLUSION

Abemaciclib plus fulvestrant was effective regardless of PIK3CA or ESR1 mutation status, with benefit in both PFS and OS, with a numerically greater improvement in median PFS relative to placebo plus fulvestrant for PIK3CA or ESR1-mutant tumors compared to the respective wild-type subgroups, in women with HR+, HER2- ABC that had progressed on ET.

Pharmacoeconomic evaluations of CDK4/6 inhibitors plus endocrine therapy for advanced hormone receptor-positive (HR+) and human epidermal growth factor receptor-2 negative (HER2-) breast cancer: a systematic review

Background

Hormone receptor-positive (HR+) and human epidermal growth factor receptor-2 negative (HER2−) breast cancer is the most common molecular subtype of breast cancer in many countries, and endocrine therapy remains a mainstay in its treatment. Cyclin-dependent kinase (CDK) 4/6 inhibitors are a new class of targeted agents administered orally that are recommended being used in combination with endocrine therapy as first and second line treatments for advanced HR+/HER2− breast cancer. However, their high prices largely hinder using these drugs in real world settings. To offer a new basis for future research, we investigated the cost-effectiveness of combinations of CDK4/6 inhibitors with endocrine therapy in the treatment of advanced HR+/HER2− breast cancer.

Methods

We systematically searched several frequently used databases and identified economic evaluations published from February 2015 to April 2021. The systematic review was performed after retrieving the literatures and extracting data based on inclusion and exclusion criteria. The quality of each selected economic evaluation was assessed by the Consolidated Health Economic Evaluation Reporting Standards (CHEERS).

Results

The literature search yielded 161 articles, among which fourteen studies (15 articles) with CHEER scores ranging from 58.33% to 87.50% entered the final analysis. Markov models were used in most studies. Based on the currently available data, CDK4/6 inhibitors plus endocrine therapy were less cost-effective in first- or second-line treatment of patients with HR+/HER2− advanced breast cancer. However, ribociclib plus letrozole was more cost-effective than palbociclib plus letrozole in the first-line treatment of postmenopausal women. The economic impacts of CDK4/6 inhibitors plus endocrine therapy in non-postmenopausal patients or second-line therapy cannot be fully evaluated due to the limited number of studies. The three most common factors affecting economic outcomes were the prices of CDK4/6 inhibitors, hazard ratios for progression-free survival and overall survival, and health status utility values.

Discussion

CDK4/6 inhibitors plus endocrine therapy have shown significantly improved efficacy outcomes in HR+/HER2− metastatic breast cancer (mBC)/advancer breast cancer (ABC) first-line and second-line treatment for endocrine-sensitive and endocrine-resistant populations, while more potential fields including neoadjuvant and adjuvant settings are being identified to benefit a wider range of breast cancer patients. Meanwhile, risk of severe adverse events that more likely to happen in patients treated with CDK4/6 inhibitors can lead to reduced life quality and higher medical costs patients need to afford. The adverse drug reaction related cost in several economic burden studies were explored to be primarily driven by hospitalizations and outpatient, and assessment of cost associated with CDK4/6 inhibitors adverse events is worth further developing. Drug wastage costs were found higher in palbociclib regimen than ribociclib regimen due to different dosing patterns. Moreover, current economic evaluations showed that ribociclib plus letrozole had better economic benefits than palbociclib plus letrozole for first-line treatment of postmenopausal women with HR+/HER2− ABC.

A narrative review of the clinical development of CDK4/6 inhibitor abemaciclib in breast cancer

Background and Objective

Advanced or metastatic breast cancer (MBC) is associated with poor prognosis and presents many challenges in medical management and treatment decisions. Anticancer drugs that act on cell cycle mechanisms have shown great potential in preclinical studies. In clinical trials, abemaciclib, a reversible ATP-competitive cyclin-dependent kinase 4/6 (CDK4/6) inhibitor developed by Eli Lilly and Company, combined with endocrine therapy (ET) were associated with superior outcomes compared with ET alone in patients with advanced or metastatic hormone receptor positive (HR+)/human epidermal growth factor receptor 2 negative (HER2-) breast cancer, representing a new standard-of-care in this population. Abemaciclib has been approved by the U.S. Food and Drug Administration (FDA) for use in HR+/HER2- MBC. In China, abemaciclib was also approved by the National Medical Products Administration (NMPA) based on findings from the MONARCH plus trial. Recently, abemaciclib have been approved as the first and only CDK4/6 inhibitor by FDA and NMPA for use in HR+/HER2-, node-positive, early breast cancer (EBC) at high risk of recurrence and Ki-67 score ≥20%. Further trials of abemaciclib are ongoing. This is an overview of the clinical development of abemaciclib in breast cancer.

Methods

We reviewed English publications in PubMed related to CDK4/6 inhibitors from 2011 to 2021.

Key Content and Findings

In this review, we summarized the mechanism, results of preclinical and clinical studies of abemaciclib, describing current indications for treatment, ongoing clinical trials, safety and tolerability, and future perspectives.

Conclusions

Abemaciclib is a unique CDK4/6 inhibitor with distinctive characteristics and promising data, which bring benefit to HR+, HER2- breast cancer patients.

Combination of Abemaciclib following Eribulin Overcomes Palbociclib-Resistant Breast Cancer by Inhibiting the G2/M Cell Cycle Phase

Breast cancer remains a leading cancer burden among women worldwide. Acquired resistance of cyclin-dependent kinase (CDK) 4/6 inhibitors occurs in almost all hormone receptor (HR)-positive subtype cases, comprising 70% of breast cancers, although CDK4/6 inhibitors combined with endocrine therapy are highly effective. CDK4/6 inhibitors are not expected to cooperate with cytotoxic chemotherapy based on the basic cytotoxic chemotherapy mode of action that inhibits rapidly proliferating cells. The palbociclib-resistant preclinical model developed in the current study investigated whether the combination of abemaciclib, CDK4/6 inhibitor with eribulin, an antimitotic chemotherapy could be a strategy to overcome palbociclib-resistant HR-positive breast cancer. The current study demonstrated that sequential abemaciclib treatment following eribulin synergistically suppressed CDK4/6 inhibitor-resistant cells by inhibiting the G2/M cell cycle phase more effectively. The current study showed the significant association of the pole-like kinase 1 (PLK1) level and palbociclib resistance. Moreover, the cumulative PLK1 inhibition in the G2/M phase by each eribulin or abemaciclib proved to be a mechanism of the synergistic effect. The synergistic antitumor effect was also supported by in vivo study. The sequential combination of abemaciclib following eribulin merits further clinical trials to overcome resistance to CDK4/6 inhibitors in HR-positive breast cancer.

Nafamostat mesylate overcomes endocrine resistance of breast cancer through epigenetic regulation of CDK4 and CDK6 expression

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Nafamostat mesylate (NM) causes apoptosis and suppresses metastasis of endocrine-resistant ER-positive breast cancer (ERPBC).

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Epigenetic downregulation of CDK4/CDK6 by NM in endocrine-resistant ERPBC via disruption of binding of H3K27Ac on promoter region.

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Combination of nafamostat mesylate and CDK4/6 inhibitor synergistically overcomes endocrine resistance of breast cancer.

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Nafamostat mesylate would be a well-efficient drug for endocrine-resistant ERPBC.

Breast cancer is common worldwide, and the estrogen receptor-positive subtype accounts for approximately 70% of breast cancer in women. Tamoxifen and fulvestrant are drugs currently used for endocrinal therapy. Breast cancer exhibiting endocrine resistance can undergo metastasis and lead to the death of breast cancer patients. Drug repurposing is an active area of research in clinical medicine. We found that nafamostat mesylate, clinically used for patients with pancreatitis and disseminated intravascular coagulation, acts as an anti-cancer drug for endocrine-resistant estrogen receptor-positive breast cancer (ERPBC). Epigenetic repression of CDK4 and CDK6 by nafamostat mesylate induced apoptosis and suppressed the metastasis of ERPBC through the deacetylation of Histone 3 Lysine 27. A combination of nafamostat mesylate and CDK4/6 inhibitor synergistically overcame endocrine resistance in ERPBC. Nafamostat mesylate might be an essential adjuvant or alternative drug for the treatment of endocrine-resistant ERPBC due to the low cost-efficiency of the CDK4/6 inhibitor.

MDM2 as a Rational Target for Intervention in CDK4/6 Inhibitor Resistant, Hormone Receptor Positive Breast Cancer

With the adoption of inhibitors of cyclin dependent kinases 4 and 6 (CDK4/6i) in combination with endocrine therapy as standard of care for the treatment of advanced and metastatic estrogen receptor positive (ER+) breast cancer, the search is now on for novel therapeutic options to manage the disease after the inevitable development of resistance to CDK4/6i. In this review we will consider the integral role that the p53/MDM2 axis plays in the interactions between CDK4/6, ERα, and inhibitors of these molecules, the current preclinical evidence for the efficacy of MDM2 inhibitors in ER+ breast cancer, and discuss the possibility of targeting the p53/MDM2 via inhibition of MDM2 in the CDK4/6i resistance setting.

Carcinogenesis of Triple-Negative Breast Cancer and Sex Steroid Hormones

Simple Summary

Triple-negative breast cancer (TNBC) lacks all of three treatment targets (estrogen receptor-α, ER-α; progesterone receptor, PgR; and human epidermal growth factor receptor 2, HER2) and is usually associated with a poor clinical outcome; however, several sex steroid receptors, such as androgen receptor (AR), ER-β, and G-protein-coupled estrogen receptor, are frequently expressed and their biological and clinical importance has been suggested. Despite the structural similarity between sex steroid hormones (androgens and estrogens) or receptors (AR and ER-β), similar signaling mechanisms of these hormones, and the coexistence of these hormones and their receptors in TNBC in a clinical setting, most studies or reviews focused on only one of these receptors, and rarely reviewed them in a comprehensive way. In this review, the carcinogenic or pathobiological role of sex steroid hormones in TNBC is considered, focusing on common and differing features of hormone actions.

Abstract

Triple-negative breast cancer (TNBC) lacks an effective treatment target and is usually associated with a poor clinical outcome; however, hormone unresponsiveness, which is the most important biological characteristic of TNBC, only means the lack of nuclear estrogenic signaling through the classical estrogen receptor (ER), ER-α. Several sex steroid receptors other than ER-α: androgen receptor (AR), second ER, ER-β, and non-nuclear receptors represented by G-protein-coupled estrogen receptor (GPER), are frequently expressed in TNBC and their biological and clinical importance has been suggested by a large number of studies. Despite the structural similarity between each sex steroid hormone (androgens and estrogens) or each receptor (AR and ER-β), and similarity in the signaling mechanisms of these hormones, most studies or reviews focused on one of these receptors, and rarely reviewed them in a comprehensive way. Considering the coexistence of these hormones and their receptors in TNBC in a clinical setting, a comprehensive viewpoint would be important to correctly understand the association between the carcinogenic mechanism or pathobiology of TNBC and sex steroid hormones. In this review, the carcinogenic or pathobiological role of sex steroid hormones in TNBC is considered, focusing on the common and divergent features of the action of these hormones.

Recent advances in the treatment of hormone receptor-positive/human epidermal growth factor 2-positive advanced breast cancer

Hormone receptor (HR)-positive/human epidermal growth factor receptor 2 (HER2)-positive (HR+/HER2+) advanced breast cancer is a special subtype of cancer with unique features. Major guidelines recommend that combination therapy containing anti-HER2 therapy (e.g., trastuzumab and pertuzumab) should be applied as the first-line treatment for HER2+ advanced breast cancer, regardless of HR status. Endocrine therapy could be relegated to patients who cannot tolerate chemotherapy or as a post-chemotherapy empirical maintenance strategy. Previous studies have shown that the HR pathway interacts with the HER2 pathway, and the HR and HER2 pathways of endocrine therapy combined with targeted therapy can effectively avoid tumor resistance. Therefore, the combination of endocrine and targeted therapies is the preferred treatment plan for HR+/HER2+ patients to replace chemotherapy. In this review, we will discuss research progress regarding endocrine therapy combined with anti-HER2 therapy in patients with advanced breast cancer, to provide more evidence for clinical practice and broader perspectives for related research. In the future, we hope there will be more studies on HR+/HER2+ advanced breast cancer to elucidate the optimal and appropriate treatment for these patients.

Advances in Therapy for Hormone Receptor (HR)-Positive, Human Epidermal Growth Factor Receptor 2 (HER2)-Negative Advanced Breast Cancer Patients Who Have Experienced Progression After Treatment with CDK4/6 Inhibitors

Approximately 70% of breast cancer (BC) cases are hormone receptor-positive (HR+) and human epidermal growth factor receptor 2-negative (HER2-) BC. Cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors have acted as star drugs for reversing endocrine therapy (ET) resistance and improving the prognosis of patients with HR+ advanced breast cancer (ABC) since they were initially approved. However, progression eventually occurs. In this review, we summarize the recent treatment strategies post CDK4/6 inhibitors: 1) CDK4/6 inhibitors plus exemestane and everolimus; 2) phosphoinositide-3-kinase (PI3K) inhibitor alpelisib plus fulvestrant for patients with PIK3CA mutation; 3) poly (ADP-ribose) polymerase (PARP) inhibitor for patients with germline PALB2 mutations, somatic BRCA1/2 mutations, or germline BRCA1/2 mutations; 4) exemestane and everolimus; and (5) chemotherapy. These strategies are all supported by evidence from clinical trials and retrospective studies. We also describe potential future treatment strategies post CDK4/6 inhibitors, such as the trophoblast cell surface antigen 2 (Trop-2) directed antibody–drug conjugate, cyclin-dependent kinase 7 (CDK7) inhibitors, and B-cell lymphoma-2 (BCL-2) inhibitors.

Thromboembolic Events with Cyclin-Dependent Kinase 4/6 Inhibitors in the FDA Adverse Event Reporting System

Simple Summary

This post-marketing research addressed the role of cyclin-dependent kinase 4/6 inhibitors, relatively new anticancer drugs approved for advanced breast cancer in cancer-associated thrombosis. We used the Food and Drug Administration pharmacovigilance database to retrospectively assess thromboembolic events in the real world. A potential class effect was found for venous thrombosis, whereas distinctive arterial events emerged for ribociclib. These signals call for both prospective research and early proactive monitoring by oncologists, also in patients without apparent risk factors. These findings strengthen the role of timely pharmacovigilance to detect and characterize post-marketing adverse events of special interest, thus supporting patient care.

Abstract

We analyzed thromboembolic events, recognized (AESIs), with cyclin-dependent kinase (CDK)4/6 inhibitors, using the Food and Drug Administration adverse event reporting system. Methods: Thromboembolic events were characterized in terms of spectrum [venous and arterial thromboembolism (VTE; ATE)] and clinical features by combining the disproportionality approach [reporting odds ratio (ROR) with 95% confidence interval (CI)] with individual case assessment. Results: A total of 1722 thromboembolic events were retained. Increased VTE reporting emerged for CDK4/6 inhibitors in the exploratory analyses (n = 659; ROR = 1.51; 95% CI = 1.39–1.63), with consistent disproportionality in the consolidated analyses (e.g., deep vein thrombosis with abemaciclib: 17; 1.98; 1.22–3.19). Higher-than-expected ATE reporting was found for ribociclib, including myocardial infarction (41; 1.82; 1.33–2.48), with rapid onset (median latency 1 vs. 6 months for other CDK4/6 inhibitors). Causality was highly probable or probable in 83.2% of cases, with a negligible proportion of pre-existing drug- and patient-related risk factors except for cardiovascular comorbidities (26%). Conclusions: Although causal association cannot be firmly inferred, oncologists should proactively monitor the occurrence of VTE with CDK4/6 inhibitors. The unexpected distinctive increased ATE reporting with ribociclib deserves urgent clarification though large comparative population-based studies. We support pharmacovigilance for the post-marketing characterization of AESIs, thus promoting real-time safe prescribing in oncology.