Overall Survival with Palbociclib and Fulvestrant in Advanced Breast Cancer

The role of ultrasonographic findings for PIK3CA-mutated, hormone receptor-positive, human epidermal growth factor receptor-2-negative breast cancer

To determine whether ultrasound (US) features of breast cancer are associated with Breast Imaging and Reporting Data System molecular subtype, histologic grade, and hormone receptor status as well as to assess the predictive value of these features. Retrospective analysis of the medical records of 220 consecutive patients with invasive breast cancer was reviewed according to the PIK3CA-mutated molecular tumor subtype. US findings of all patients were analyzed. Breast tumors harboring a PIK3CA-mutation were large and exhibited liquefied necrosis and posterior echo attenuation in the nodule. Moreover, such tumors were lobulated and calcified. The aspect ratio of the PIK3CA-mutant was more likely >1. The average nodule elasticity (7.479 ± 0.993 m/s) was measured using US shear wave elastography. Microcalcification was easier to detect inside the nodule using a fluorescence technique. Measurement of the nodule blood flow spectrum showed that the internal blood flow resistance index of nodules was lower than that of other types of breast cancer. The sonographic features of PIK3CA-mutated breast cancers were strongly associated with extensive and liquefied necrosis. The ability to predict molecular subtypes, particularly using US to detect the triple-negative subtype, may play an important role in early management and treatment.

Detection of high-risk patients resistant to CDK4/6 inhibitors with hormone receptor-positive HER2-negative advanced and metastatic breast cancer in Japan (KBCSG-TR-1316)

BACKGROUND

Cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) improve the prognosis of hormone receptor-positive HER2-negative advanced/metastatic breast cancer (HR+/HER2- mBC). However, some cancers show resistance to CDK4/6i and have a poor prognosis. The non-luminal disease score (NOLUS) was developed to predict non-luminal disease using immunohistochemical analysis.

METHODS

The association between the efficacy of CDK4/6i and NOLUS was investigated by evaluating pathological and clinical data, including real-world progression-free survival (rw-PFS) and overall survival (OS). Real-world data of patients with HR+/HER2- mBC who received CDK4/6i therapy [palbociclib or abemaciclib] as first- or second-line endocrine treatments was obtained. NOLUS was calculated using the formula: NOLUS (0-100) = - 0.45 × estrogen receptor (ER) (%) - 0.28 × progesterone receptor (PR) (%) + 0.27 × Ki67(%) + 73, and the patients were divided into two groups: NOLUS-positive (≥ 51.38) and NOLUS-negative (< 51.38).

RESULTS

Of the 300 patients, 28 (9.3%) were NOLUS-positive, and 272 (90.7%) were NOLUS-negative. The expression rates (%) of ER and PgR in NOLUS-positive patients were lower than those in NOLUS-negative patients (p < 0.001). Ki67 expression was higher in NOLUS-positive patients. There were statistically significant differences in prognosis (rw-PFS and OS) between the two groups. Moreover, NOLUS-negative patients showed statistically better rw-PFS with first-line therapy than second-line therapy. However, NOLUS-positive patients showed poor prognoses with both the first and second therapeutic lines, suggesting CDK4/6i inefficacy for NOLUS-positive patients.

CONCLUSIONS

The efficacy and prognosis of CDK4/6i significantly differed between the NOLUS-positive and NOLUS-negative patients. This feasible method can predict patients with HR+/HER2- mBC resistant to CDK4/6i and help select a better therapeutic approach to overcome resistance.

The Japanese Breast Cancer Society Clinical Practice Guidelines for systemic treatment of breast cancer, 2022 edition

The Japanese Breast Cancer Society (JBCS) Clinical Practice Guidelines for systemic treatment of breast cancer were updated to the 2022 edition through a process started in 2018. The updated guidelines consist of 12 background questions (BQs), 33 clinical questions (CQs), and 20 future research questions (FRQs). Multiple outcomes including efficacy and safety were selected in each CQ, and then quantitative and qualitative systematic reviews were conducted to determine the strength of evidence and strength of recommendation, which was finally determined through a voting process among designated committee members. Here, we describe eight selected CQs as important updates from the previous guidelines, including novel practice-changing updates, and recommendations based on evidence that has emerged specifically from Japanese clinical trials.

Surrogate endpoints for HTA decisions of breast cancer drugs: utility and pitfalls

PURPOSE OF REVIEW

Health technology assessment (HTA) of cancer drugs is important to identify whether drugs should be publicly funded. With increasing use of surrogate end points in clinical trials including breast cancer, a review of literature was done to synthesize evidence for validation of these surrogate end points and their potential role in HTA decisions pertaining to breast cancer.

FINDINGS

Disease free survival (DFS) in human epidermal receptor 2 (HER2) positive early breast cancer remains the only validated surrogate end point. Other surrogate end points like pathological complete response (pCR) and event free survival (EFS) in early breast cancer (EBC) and objective response rate (ORR) and progression free survival (PFS) in advanced disease have not been validated for overall survival (OS). Moreover, surrogate end points for quality of life (QOL) have not been established and drugs that improve PFS can have detrimental effect on QOL. End points like pCR have excellent prognostic utility in individual patients but have weak correlation with survival at trial level.

SUMMARY

Most surrogate end points used in breast cancer do not predict OS or QOL which makes it challenging to use them for decisions regarding public funding of cancer drugs. These findings are relevant to HTA agencies prior to making drug reimbursement decisions.

Efficacy of Oral SERDs in the treatment of ER+, HER2 - metastatic breast cancer, a stratified analysis of the ESR1 wild type and mutant subgroups

BACKGROUND

Oral SERDs are a novel drug class that have been developed to counteract resistance due to ESR1 mutations. Several SERDs have emerged from phase 2 and 3 trials, with the FDA limiting approval for Elacestrant to patients with ESR1mt tumours despite PFS benefit in the overall population. However, questions remain on whether patients with ESR1wt tumours stand to benefit from oral SERDs.

PATIENTS AND METHODS

Manuscripts and conference presentations of Randomised Controlled Trials were extracted after a systematic search of Embase, PubMed and Cochrane from inception until January 21,2023. RCTs investigating the efficacy of oral SERDs versus endocrine therapy for ER positive, HER2 negative advanced breast cancer, and which reported the Kaplan Meier (KM) curves of PFS in the overall and ESR1 mutant (ESR1mt) population were selected. A graphical reconstructive algorithm was applied to estimate time-to-event outcomes from reported KM curves in all overall and ESR1mt cohorts. A bipartite matching algorithm, KMSubtraction, was used to derive survival data for unreported (ESR1wt) subgroups. An individual patient data (IPD) meta-analysis was then pursued, pooling data by ESR1 mutation status in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) and Cochrane Guidelines for IPD.

RESULTS

The randomized clinical trials ACELERA, AMEERA-3, EMERALD and SERENA-2 were included, totalling 1290 patients. In the pooled analysis of the overall cohort, PFS benefit was observed with oral SERDs when compared with treatment of physicians choice (TPC) (HR 0.783, 95%CI 0.681-0.900, p<0.001). In the ESR1mt subgroup, oral SERDs demonstrated improved PFS (HR 0.557, 95%CI 0.440-0.705, p<0.001) compared to TPC. In the ESR1wt subgroup, oral SERDs demonstrated no significant PFS benefit (HR 0.944, 95%CI 0.783-1.138, p=0.543) when compared to TPC.

CONCLUSIONS

The results of this IPD meta-analysis suggests that PFS benefit in the overall population is mainly driven by the ESR1mt subgroup.

CDK4/6 inhibitors: basics, pros, and major cons in breast cancer treatment with specific regard to cardiotoxicity - a narrative review

Breast cancer is characterized by the uncontrolled proliferation of breast cells, with a high incidence reported in 2020 to have affected over 2 million women. In recent years, the conventional methods of treating breast cancer have involved radiotherapy and chemotherapy. However, the emergence of CDK4/6 inhibitors has shown potential as a promising cancer therapy. Cyclin-dependent kinases (CDK) inhibitors are a class of molecules that impede the formation of an active kinase complex, thereby hindering its activity and consequently halting the progression of the cell cycle. It was discovered that they have a significant impact on impeding the progression of the cancer. This is evident with the Food and Drug Administration's approval of drugs such as palbociclib, ribociclib, and abemaciclib for hormone receptor-positive metastatic breast cancer in combination with specific endocrine therapies. In spite of enormous success in breast cancer treatment, certain obstacles have emerged, such as therapy resistance, side effects, and most of all, cardiotoxicity. Some of these drawbacks have been successfully overcome by dosage reduction, different combinations of the drugs, and the assessment of each patient's condition and suitability prior to treatment. Yet other drawbacks still require tenacious research, especially certain cases of cardiotoxicities. This article delves into the biological mechanisms of CDK4/6 in the cell cycle and cancer, as well as the clinical advantages and most common adverse events (AEs) associated with CDK4/6 inhibitors. The primary objective of this review is to provide a comprehensive analysis of cardiotoxic AEs and elucidate the underlying pathophysiological mechanisms responsible for the cardiotoxicity of CDK4/6 inhibitors.

Timing and Reporting of Secondary Overall Survival End Points for Phase III Trials in Advanced/Metastatic Disease

Recent therapeutic advances have led to improved patient survival in many cancer settings. Although prolongation of survival remains the ultimate goal of cancer treatment, the availability of effective salvage therapies could make definitive phase III trials with primary overall survival (OS) end points difficult to complete in a timely manner. Therefore, to accelerate development of new therapies, many phase III trials of new cancer therapies are now designed with intermediate primary end points (eg, progression-free survival in the metastatic setting) with OS designated as a secondary end point. We review recently published phase III trials and assess contemporary practices for designing and reporting OS as a secondary end point. We then provide design and reporting recommendations for trials with OS as a secondary end point to safeguard OS data integrity and optimize access to the OS data for patient, clinician, and public-health stakeholders.

Quality of Life and Treatment-Related Side Effects in Patients With HR+/HER2- Advanced Breast Cancer: Findings From a Multicountry Survey

BACKGROUND

Quality of life (QOL) is a critical factor in decision-making for advanced breast cancer (ABC). There is a need to improve how QOL and treatment-related side effects (SEs) that impact it are clinically assessed. We examined healthcare professionals' (HCPs') and patients' perspectives on the importance of QOL discussions and the impact of SEs on QOL in clinical settings.

PATIENTS AND METHODS

A cross-sectional online survey was conducted (7/2020-5/2021) among oncologists, nurses, and patients with HR+/HER2- ABC in 7 countries.

RESULTS

The survey was completed by 502 HCPs and 467 patients. Overall, 88% of oncologists and 49% of patients recalled QOL discussions at follow-up. In the first- through fourth-line (1L, 2L, 3L, and 4L) settings, respectively, 48%, 57%, 79%, and 85% of oncologists reported QOL was very important; 73% and 45% of patients receiving 1L and 2L treatment and 40% receiving 3L+ treatment indicated QOL was important. Patients reported that insomnia, anxiety, back pain, fatigue, diarrhea, hot flashes, low sexual interest, and loss of appetite had a moderate/severe impact on QOL. Of patients experiencing certain SEs, ≥64% did not discuss them with HCPs until there was a moderate/severe impact on QOL. In patients receiving a CDK4/6 inhibitor, SEs, including insomnia, diarrhea, back pain, and fatigue, had a moderate/severe impact on QOL.

CONCLUSIONS

This survey discovered disconnects between HCPs and patients with ABC on the importance of QOL discussions and the impact of SEs on QOL. These data support the use of ABC-specific QOL questionnaires that closely monitor SEs impacting QOL.

Kinome Reprogramming Is a Targetable Vulnerability in ESR1 Fusion-Driven Breast Cancer

Transcriptionally active ESR1 fusions (ESR1-TAF) are a potent cause of breast cancer endocrine therapy (ET) resistance. ESR1-TAFs are not directly druggable because the C-terminal estrogen/anti-estrogen-binding domain is replaced with translocated in-frame partner gene sequences that confer constitutive transactivation. To discover alternative treatments, a mass spectrometry (MS)-based kinase inhibitor pulldown assay (KIPA) was deployed to identify druggable kinases that are upregulated by diverse ESR1-TAFs. Subsequent explorations of drug sensitivity validated RET kinase as a common therapeutic vulnerability despite remarkable ESR1-TAF C-terminal sequence and structural diversity. Organoids and xenografts from a pan-ET-resistant patient-derived xenograft model that harbors the ESR1-e6>YAP1 TAF were concordantly inhibited by the selective RET inhibitor pralsetinib to a similar extent as the CDK4/6 inhibitor palbociclib. Together, these findings provide preclinical rationale for clinical evaluation of RET inhibition for the treatment of ESR1-TAF-driven ET-resistant breast cancer.

SIGNIFICANCE

Kinome analysis of ESR1 translocated and mutated breast tumors using drug bead-based mass spectrometry followed by drug-sensitivity studies nominates RET as a therapeutic target. See related commentary by Wu and Subbiah, p. 3159.

The Evolving Pathways of the Efficacy of and Resistance to CDK4/6 Inhibitors in Breast Cancer

The approval of cyclin-dependent kinase 4 and 6 inhibitors (CDK4/6i) in combination with endocrine therapy (ET) has remarkably improved the survival outcomes of patients with advanced hormone receptor-positive (HR+) breast cancer (BC), becoming the new standard of care treatment in these patients. Despite the efficacy of this therapeutic combination, intrinsic and acquired resistance inevitably occurs and represents a major clinical challenge. Several mechanisms associated with resistance to CDK4/6i have been identified, including both cell cycle-related and cell cycle-nonspecific mechanisms. This review discusses new insights underlying the mechanisms of action of CDK4/6i, which are more far-reaching than initially thought, and the currently available evidence of the mechanisms of resistance to CDK4/6i in BC. Finally, it highlights possible treatment strategies to improve CDK4/6i efficacy, summarizing the most relevant clinical data on novel combination therapies involving CDK4/6i.

Breast cancers arising in subjects with germline BRCA1 or BRCA2 mutations: Different biological and clinical entities with potentially diverse therapeutic opportunities

Breast cancers (BCs) arising in carriers of germline BRCA1 and BRCA2 pathogenic variants (PVs) have long been considered as indistinguishable biological and clinical entities. However, the loss of function of BRCA1 or BRCA2 proteins has different consequences in terms of tumor cell reliance on estrogen receptor signaling and tumor microenvironment composition. Here, we review accumulating preclinical and clinical data indicating that BRCA1 or BRCA2 inactivation may differentially affect BC sensitivity to standard systemic therapies. Based on a different crosstalk between BRCA1 or BRCA2 and the ER pathway, BRCA2-mutated Hormone Receptor-positive, HER2-negative advanced BC may be less sensitive to endocrine therapy (ET) plus CDK 4/6 inhibitors (CDK 4/6i), whereas BRCA2-mutated triple-negative breast cancer (TNBC) may be especially sensitive to immune checkpoint inhibitors. If validated in future prospective studies, these data may have relevant clinical implications, thus establishing different treatment paths in patients with BRCA1 or BRCA2 PVs.

The role of CDK4/6 inhibitors in older and younger patients with breast cancer: A systematic review and meta-analysis

INTRODUCTION

Cyclin-dependent kinase 4/6 (CDK4/6) inhibitors have an extremely important impact on the treatment of hormone-sensitive breast cancer (BC) and have radically changed the first-line treatment for metastatic disease with increased rates of treatment response, overall survival (OS), and progression-free survival (PFS). We performed a pooled analysis of randomized trials to validate or refute the hypothesis that there is a significant survival benefit of adding anti-CDK4/6 inhibitors to standard endocrine therapy (ET) in older patients with advanced BC.

METHODS

We selected only English-language phase II/III randomized controlled trials that compared ET alone with ET with anti-CDK4/6 inhibitors in the treatment of advanced BC, with subgroups reporting the outcomes of elderly patients (usually at least 65 years). The primary endpoint was OS.

RESULTS

The review process led to the inclusion of 12 articles and two meeting abstracts, including a total of 10 trials. The addition of CDK4/6 inhibitors to ET (letrozole or fulvestrant) significantly reduced mortality risk by 20% in younger patients (fixed-effect model; HR 0.80; 95% CI 0.72-0.9; p < 0.01) and 21% in older BC patients (HR 0.79; 95% CI 0.69-0.91; p < 0.01). No OS data were available for patients ≥70 years.

CONCLUSION

This large, pooled analysis is the first to demonstrate that CDK4/6 inhibitors confer OS and PFS benefits in elderly patients (those aged ≥65 years) with advanced ER + BC and to indicate that it should be discussed with and offered to all patients after geriatric assessment and according to the toxicity profile.

[Venous thromboembolism and breast cancer]

Breast cancer is the most common cancer in women. Patients with breast cancer have a 4-fold increased risk of venous thromboembolism (VTE) compared to age- and sex-matched controls without cancer. VTE remains the second leading cause of death in cancer patients and an independent risk factor for mortality. In women with breast cancer, the main risk factors for developing VTE are increasing age, obesity, disease stage, central catheter placement and cancer treatments, including surgery, chemotherapy, hormonotherapy and cyclin-dependent kinase 4/6 inhibitors. In women receiving tamoxifen, the risk of VTE is particularly increased within the first 6 months after initiation of hormonotherapy, although some evidence suggests that this risk may persist through the first 2 years of treatment. The risk of VTE appears to be lower in patients receiving aromatase inhibitors. In breast cancer patients receiving cyclin-dependent kinase 4/6 inhibitors, the rate of VTE is approximately 6%. Current clinical practice guidelines for the treatment and prevention of VTE in patients with cancer suggest that thromboprophylaxis should not be used routinely in ambulatory cancer patients receiving chemotherapy or hormonotherapy. The risk-benefit ratio of thromboprophylaxis should be assessed on a case-by-case basis and be the subject of multidisciplinary discussion.

Outcomes and toxicity of concurrent CDK4/6 inhibitor and locoregional radiotherapy for patients with de novo metastatic breast cancer

The objective of the present study was to assess the outcomes and toxicity of patients treated with concurrent administration of CDK4/6 inhibitors (CDK4/6i) and locoregional radiation therapy (RT), including the breast with a boost or the thoracic wall after mastectomy and the regional lymph node areas. We retrospectively analyzed data from 27 patients with hormone receptor-positive, HER2-negative de novo metastatic breast cancer treated with CDK4/6i and concomitant locoregional RT in 2017/2022. Survival rates were calculated by Kaplan-Meier method. Prognostic factors were tested with log-rank test. CDK4/6i was used as the first systemic metastatic treatment for all the patients, and the median overall treatment time was 26 months. The median time from initiation of CDK4/6i to the start of RT was 10 months (IQR: 7-14 months). The median duration of concomitant CDK4/6i and RT administration was 21 days (IQR: 14.5-23 days). After a median follow-up of 19 months (IQR: 14-36 months), 1 patient died, 11/27 had distant metastases and 1 patient had local recurrence, respectively. The 1- and 3-years progression-free survival (PFS) were 61.4% (95% CI: 45.1%-83.7%) and 53.7% (35.8%-80.5%), respectively. The acute toxicities most observed during RT were neutropenia (44%) and dermatitis (37%). Dermatitis was significantly more frequent in patients with large target volumes (CTV > 911 cc and PTV > 1285 cc). CDK4/6i had to be discontinued in five patients during RT (due to toxicity in three cases and disease progression in two cases). One patient has developed grade 2 late pulmonary fibrosis. Finally, our study demonstrated that concurrent administration of locoregional RT and CDK4/6i did not induce severe late toxicity for most patients.

Molecular classification of hormone receptor-positive HER2-negative breast cancer

Hormone receptor-positive (HR+)/human epidermal growth factor receptor 2-negative (HER2-) breast cancer is the most prevalent type of breast cancer, in which endocrine therapy resistance and distant relapse remain unmet challenges. Accurate molecular classification is urgently required for guiding precision treatment. We established a large-scale multi-omics cohort of 579 patients with HR+/HER2- breast cancer and identified the following four molecular subtypes: canonical luminal, immunogenic, proliferative and receptor tyrosine kinase (RTK)-driven. Tumors of these four subtypes showed distinct biological and clinical features, suggesting subtype-specific therapeutic strategies. The RTK-driven subtype was characterized by the activation of the RTK pathways and associated with poor outcomes. The immunogenic subtype had enriched immune cells and could benefit from immune checkpoint therapy. In addition, we developed convolutional neural network models to discriminate these subtypes based on digital pathology for potential clinical translation. The molecular classification provides insights into molecular heterogeneity and highlights the potential for precision treatment of HR+/HER2- breast cancer.

Recent Developments in the Therapeutic Landscape of Advanced or Metastatic Hormone Receptor-Positive Breast Cancer

Hormone receptor-positive (HR+) disease is the most frequently diagnosed subtype of breast cancer. Among tumor subtypes, natural course of HR+ breast cancer is indolent with favorable prognosis compared to other subtypes such as human epidermal growth factor protein 2-positive disease and triple-negative disease. HR+ tumors are dependent on steroid hormone signaling and endocrine therapy is the main treatment option. Recently, the discovery of cyclin-dependent kinase 4/6 inhibitors and their synergistic effects with endocrine therapy has dramatically improved treatment outcome of advanced HR+ breast cancer. The demonstrated efficacy of additional nonhormonal agents, such as targeted therapy against mammalian target of rapamycin and phosphatidylinositol 3-kinase signaling, poly(ADP-ribose) polymerase inhibitors, antibody-drug conjugates, and immunotherapeutic agents have further expanded the available therapeutic options. This article reviews the latest advancements in the treatment of HR+ breast cancer, and in doing so discusses not only the development of currently available treatment regimens but also emerging therapies that invite future research opportunities in the field.

Efficacy of Limited Dose Modifications for Palbociclib-Related Grade 3 Neutropenia in Hormone Receptor-Positive Metastatic Breast Cancer

PURPOSE

Frequent neutropenia hinders uninterrupted palbociclib treatment in patients with hormone receptor (HR)-positive breast cancer. We compared the efficacy outcomes in multicenter cohorts of patients with metastatic breast cancer (mBC) receiving palbociclib following conventional dose modification or limited modified schemes for afebrile grade 3 neutropenia.

MATERIALS AND METHODS

Patients with HR-positive, human epidermal growth factor receptor 2-negative mBC (n=434) receiving palbociclib with letrozole as first-line therapy were analyzed and classified based on neutropenia grade and afebrile grade 3 neutropenia management as follows: group 1 (maintained palbociclib dose, limited scheme), group 2 (dose delay or reduction, conventional scheme), group 3 (no afebrile grade 3 neutropenia event), and group 4 (grade 4 neutropenia event). The primary and secondary endpoints were progression-free survival (PFS) between groups 1 and 2 and PFS, overall survival, and safety profiles among all groups.

RESULTS

During follow-up (median 23.7 months), group 1 (2-year PFS, 67.9%) showed significantly longer PFS than did group 2 (2-year PFS, 55.3%; p=0.036), maintained across all subgroups, and upon adjustment of the factors. Febrile neutropenia occurred in one and two patients of group 1 and group 2, respectively, without mortality.

CONCLUSION

Limited dose modification for palbociclib-related grade 3 neutropenia may lead to longer PFS, without increasing toxicity, than the conventional dose scheme.

Hounsfield Units Predict Survival of Patients With Estrogen Receptor-Positive and Human Epithelial Growth Factor Receptor 2-Negative Breast Cancer

BACKGROUNDS

Tumor vascularity plays a fundamental role in cancer progression, including breast cancer. This study aimed to elucidate tumor vascularity and its impact on patient survival in the context of breast cancer subtypes using Hounsfield units (HU) on contrast-enhanced computed tomography (CT).

MATERIALS AND METHODS

Patients with early-stage breast cancer who completed planned treatment between 2003 and 2013 were retrospectively assessed.

RESULTS

The final cohort comprised 440 patients. Of the 440 patients, 262 had estrogen receptor (ER)-positive disease and 119 had human epidermal growth factor receptor 2 (HER2)-overexpressing disease. The tumor-to-aorta ratio of Hounsfield units (TAR) was related to significantly worse recurrence-free interval (RFI) (P < .001) and overall survival (OS) (P < .001) in patients with TAR > 0.33 for RFI and > 0.35 for OS than their counterparts. In the subgroup analysis, the survival disadvantage was limited only to patients with ER-positive and HER2-negative disease (P < .001 for both RFI and OS).

CONCLUSION

This study showed that TAR, which reflects tumor vascularity, was significantly related to patients' RFI and OS, suggesting its capacity as a feasible biomarker. This study also showed that TAR was associated with the survival in patients with ER-positive and HER2-negative disease.

Estrogen Receptor Signaling in Breast Cancer

Estrogen receptor (ER) signaling is a critical regulator of cell proliferation, differentiation, and survival in breast cancer (BC) and other hormone-sensitive cancers. In this review, we explore the mechanism of ER-dependent downstream signaling in BC and the role of estrogens as growth factors necessary for cancer invasion and dissemination. The significance of the clinical implications of ER signaling in BC, including the potential of endocrine therapies that target estrogens' synthesis and ER-dependent signal transmission, such as aromatase inhibitors or selective estrogen receptor modulators, is discussed. As a consequence, the challenges associated with the resistance to these therapies resulting from acquired ER mutations and potential strategies to overcome them are the critical point for the new treatment strategies' development.

An Overview of the Safety Profile and Clinical Impact of CDK4/6 Inhibitors in Breast Cancer-A Systematic Review of Randomized Phase II and III Clinical Trials

Cyclin-dependent kinase 4 and 6 inhibitors (CDK4/6is) have transformed the treatment of hormone receptor-positive (HR+) and human epidermal growth factor receptor 2-negative (HER2-) breast cancer over the last decade. These inhibitors are currently established as first- and second-line systemic treatment choices for both endocrine-sensitive and -resistant breast cancer populations alongside endocrine therapy (ET) or monotherapy. Data on targeted therapy continue to mature, and the number of publications has been constantly rising. Although these drugs have been demonstrated to prolong overall survival (as well as progression-free survival (PFS) in breast cancer patients), changing the paradigm of all current knowledge, they also cause important adverse events (AEs). This review provides the latest summary and update on the safety profile of the three CDK4/6 inhibitors, as it appears from all major phase II and III randomized clinical trials regarding palbociclib, ribociclib, and abemaciclib, including the most relevant 15 clinical trials.

Nuclear Estrogen Receptors in Prostate Cancer: From Genes to Function

Estrogens are almost ubiquitous steroid hormones that are essential for development, metabolism, and reproduction. They exert both genomic and non-genomic action through two nuclear receptors (ERα and ERβ), which are transcription factors with disregulated functions and/or expression in pathological processes. In the 1990s, the discovery of an additional membrane estrogen G-protein-coupled receptor augmented the complexity of this picture. Increasing evidence elucidating the specific molecular mechanisms of action and opposing effects of ERα and Erβ was reported in the context of prostate cancer treatment, where these issues are increasingly investigated. Although new approaches improved the efficacy of clinical therapies thanks to the development of new molecules targeting specifically estrogen receptors and used in combination with immunotherapy, more efforts are needed to overcome the main drawbacks, and resistance events will be a challenge in the coming years. This review summarizes the state-of-the-art on ERα and ERβ mechanisms of action in prostate cancer and promising future therapies.

The Treatment Landscape of Elderly Patients with Hormone Receptor-Positive Her2 Negative Advanced Breast Cancer: Current Perspectives and Future Directions

Breast cancer (BC) in elderly women is an increasing health issue due to demographic changes. BC tends to present later and may receive less than standard treatment options. More often, BC in elderly patients is endocrine-positive (HR+). The treatment of elderly patients with metastatic BC (mBC) represents a therapeutic challenge. In recent years, the treatment landscape of patients that are HR+/Her2-negative has changed due to the introduction in clinical practice of new targeted drugs, which have improved patient outcomes. Elderly patients are a small percentage of all patients enrolled in clinical trials and, to date, there are no standardized guidelines that define the best treatment option for this patient population. This can lead to undertreatment or overtreatment, impacting patient morbidity and mortality. Geriatric Assessment tools to tailor the treatment in elderly patients are underused because they are long and difficult to apply in a busy routine clinical practice. For all these reasons, there is an urgent need to produce data about the best treatment for elderly patients with HR+ mBC. Herein, we report data from randomized clinical trials and real-world evidence on the therapeutic options for HR+ Her2-negative mBC elderly patients and explore future treatment directions.

Safety profile of cyclin-dependent kinase (CDK) 4/6 inhibitors with concurrent radiation therapy: A systematic review and meta-analysis

The cyclin-dependent kinase 4 and 6 inhibitors (CDK4/6i) have become the standard of care for hormone receptor-positive (HR + ) and human epidermal growth factor receptor 2-negative (HER2-) metastatic breast cancer, improving survival outcomes compared to endocrine therapy alone. Abemaciclib and ribociclib, in combination with endocrine therapy, have demonstrated significant benefits in invasive disease-free survival for high-risk HR+/HER2- early breast cancer patients. Each CDK4/6i-palbociclib, ribociclib, and abemaciclib-exhibits distinct toxicity profiles. Radiation therapy (RT) can be delivered with a palliative or ablative intent, particularly using stereotactic body radiation therapy for oligometastatic or oligoprogressive disease. However, pivotal randomized trials lack information on concomitant CDK4/6i and RT, and existing preclinical and clinical data on the potential combined toxicities are limited and conflicting. As part of a broader effort to establish international consensus recommendations for integrating RT and targeted agents in breast cancer treatment, we conducted a systematic review and meta-analysis to evaluate the safety profile of combining CDK4/6i with palliative and ablative RT in both metastatic and early breast cancer settings.

Effectiveness and Safety of Palbociclib Plus Endocrine Therapy in Patients with Advanced Breast Cancer: A Multi-Center Study in China

BACKGROUND

Palbociclib has been approved for marketing in China. However, its effectiveness, safety, and latent variables in the Chinese population require further investigation.

METHODS

Information was retrieved from 397 patients with metastatic breast cancer (mBC) who received at least two cycles of palbociclib plus endocrine therapy (PAL plus ET) at eight clinical sites in China. The patients' demographic characteristics, treatment patterns, and adverse events (AEs) were analyzed.

RESULTS

The objective response rate (ORR) and clinical benefit rate (CBR) for PAL plus ET were 28.97% and 66.25%, respectively. The median PFS was 14.2 months in the whole population. In addition to protein Ki-67 status and sensitivity to ETs, no liver metastases, fewer metastatic sites, an earlier line of therapy, and treatment combined with AI instead of FUL were also considered as independent prognostic factors for PAL treatment. Administration of PAL was generally well tolerated in patients with hormone-receptor-positive and human-epidermal-growth-factor-receptor-2-negative (HR+/HER2-) advanced breast cancer (ABC). The therapy was safe in the elderly population, which is consistent with the outcomes of the whole population and previous reports.

CONCLUSIONS

In this most widely distributed study in China to date, palbociclib combined with ET proved its effectiveness for HR+/HER2- ABC treatment, and adverse events were manageable. Here, we identified some independent prognosis factors, but the mechanism by which these factors influence effectiveness requires further verification.

CDK4/6i enhances the antitumor effect of PD1 antibody by promoting TLS formation in ovarian cancer

Ovarian cancer is insensitive to immunotherapy and has a high mortality rate. CDK4/6 inhibitors (CDK4/6i) regulate the tumor microenvironment and play an antitumor role. Our previous research demonstrated that lymphocyte aggregation (tertiary lymphoid structures, TLSs) was observed after CDK4/6i treatment. This may explain the synergistic action of CDK4/6i with the anti-PD1 antibody. However, the key mechanism by which CDK4/6i promotes TLS formation has not been elucidated. We examine the link between TLS and prognosis. Animal models and high-throughput sequencing were used to explore the potential mechanism by which CDK4/6i promotes TLS formation. Our results showed the presence of TLSs was associated with a favorable prognosis for ovarian cancer. CDK4/6i promoted TLS formation and enhanced the immunotherapeutic effect of the anti-PD1 antibody. The potential mechanism of CDK4/6i affecting the formation of TLS may be through modulating SCD1 and its regulatory molecules ATF3 and CCL4. Our findings provide a theoretical basis for the application of CDK4/6i in ovarian cancer.

Characterization of the Tumor Microenvironment of De Novo Oligometastatic Breast Cancer in a Nationwide Cohort

PURPOSE

Oligometastatic breast cancer (OMBC) has a more favorable outcome than widespread metastatic breast cancer. Some patients with OMBC achieve long-term remission if treated with multimodality therapy, including systemic and locally ablative therapies. However, not all patients with OMBC benefit from such treatment, while all experience toxicity. To explore biomarkers identifying patients with OMBC and potential long-term survival, we compared tumor-immune characteristics of patients with OMBC and long-term versus shorter-term survival.

MATERIALS AND METHODS

We collected tumor tissue of 97 patients with de novo OMBC (≤5 metastases) via the Dutch nationwide cancer and pathology registries using a case-control design. Long-term survivors (LTS) were defined as patients alive ≥10 years since OMBC diagnosis. Fifty-five LTS and 42 shorter-term survivors (STS) were included. Median follow-up was 15 years (IQR, 14-16). Tumor characteristics and infiltrating immune cells were assessed by immunohistochemistry and next-generation RNA-sequencing. Association of the resulting 52 biomarkers with long-term survival was assessed using logistic regression. Associations with survival within LTS were assessed using Cox-proportional hazards modeling. P values were adjusted for multiple hypothesis testing.

RESULTS

Most patients had estrogen receptor (ER)-positive OMBC (n = 86; 89%) and 23 (24%) had human epidermal growth factor receptor 2-positive disease. ER positivity in primary tumors distinguished LTS from STS. In addition, extracellular matrix (ECM)2-low and ECM4-high distinguished between long-term and shorter-term survival. Immune levels in the primary tumor did not associate with LTS. However, within the LTS subset, higher immune levels associated with improved progression-free survival.

CONCLUSION

We identified tumor and ECM features in the primary tumor of patients with de novo OMBC that were associated with long-term survival. Our data should be validated in other patients with OMBC before they can be used in clinical practice.

CDK4/6 Inhibition in the Metastatic Setting: Where Are We Headed?

OPINION STATEMENT

Hormone receptor positive (HR+), human epidermal growth factor receptor 2 negative (HER-2-) metastatic breast cancer (MBC) is the most common subtype of breast cancer. Due to therapeutic advances with molecularly targeted therapies, the prognosis for patients with metastatic disease has improved significantly. The advent of CDK4/6 inhibitors (CDK4/6i) has changed the treatment paradigm for patients with HR+HER2-MBC. CDK4/6i allowed for marked improvement in overall survival, delaying the time to chemotherapy initiation, and improved quality of life for our patients. Efforts are now focused on the best approach(es) for patients after progression on CDK4/6i. Can we further harness the benefit of CDK4/6i in novel combinations at the time of progression? Should we continue CDK4/6i or proceed other novel agents or endocrine therapies? As we advance our treatment strategies for HR+HER2-MBC, there is no longer a one-size-fits-all model, but instead a multifaceted and personalized approach lending to improved outcomes for our patients.

Prognostic and predictive biomarkers with therapeutic targets in breast cancer: A 2022 update on current developments, evidence, and recommendations

OBJECTIVE

To evaluate and validate the recent and emerging data for prognostic and predictive biomarkers with therapeutic targets in breast cancer.

DATA SOURCES

A literature search from January 2015 to March 2022 was performed using the key terms breast cancer, clinical practice guidelines, gene mutations, genomic assay, immune cancer therapy, predictive and/or prognostic biomarkers, and targeted therapies.

STUDY SELECTION AND DATA EXTRACTION

Relevant clinical trials, meta-analyses, seminal articles, and published evidence- and consensus-based clinical practice guidelines in the English language were identified, reviewed and evaluated.

DATA SYNTHESIS

Breast cancer is a biologically heterogeneous disease, leading to wide variability in treatment responses and survival outcomes. Biomarkers for breast cancer are evolving from traditional biomarkers in immunohistochemistry (IHC) such as estrogen receptor (ER), progesterone receptor (PR) and epidermal growth factor receptor type 2 (HER2) to genetic biomarkers with therapeutic implications (e.g. breast cancer susceptibility gene 1/2 [BRCA1/2], estrogen receptor α [ESR1] gene mutation, HER2 gene mutation, microsatellite instability [MSI], phosphatidylinositol 3-kinase catalytic subunit 3Cα [PIK3CA] gene mutation, neurotrophic tyrosine receptor kinase [NTRK] gene mutation). In addition, current data are most robust for biomarkers in immunotherapy (e.g. programmed cell death receptor ligand-1 [PD-L1], microsatellite instability-high [MSI-H] or deficient mismatch repair [dMMR]). Oncotype DX assay remains the best validated gene expression assay that is both predictive and prognostic whereas MammaPrint is prognostic for genomic risk.

CONCLUSIONS

Biomarker-driven therapies have the potential to confer greater therapeutic advantages than standard-of-care therapies. The purported survival benefits associated with biomarker-driven therapies should be weighed against their potential harms.

Updated overall survival from the MONALEESA-3 trial in postmenopausal women with HR+/HER2- advanced breast cancer receiving first-line ribociclib plus fulvestrant

BACKGROUND

The phase III MONALEESA-3 trial included first- (1L) and second-line (2L) patients and demonstrated a significant overall survival (OS) benefit for ribociclib + fulvestrant in patients with hormone receptor-positive, human epidermal growth factor receptor 2-negative (HR+/HER2-) advanced breast cancer (ABC) in the final protocol-specified and exploratory (longer follow-up) OS analyses. At the time of these analyses, the full OS benefit of 1L ribociclib was not completely characterized because the median OS (mOS) was not reached. As CDK4/6 inhibitor (CDK4/6i) + endocrine therapy (ET) is now a preferred option for 1L HR+/HER2- ABC, we report an exploratory analysis (median follow-up, 70.8 months; 14.5 months longer than the prior analysis) to fully elucidate the OS benefit in the MONALEESA-3 1L population.

METHODS

Postmenopausal patients with HR+/HER2- ABC were randomized 2:1 to 1L/2L fulvestrant + ribociclib or placebo. OS in 1L patients (de novo disease or relapse > 12 months from completion of [neo]adjuvant ET) was assessed by Cox proportional hazards model and Kaplan-Meier methods. Progression-free survival 2 (PFS2) and chemotherapy-free survival (CFS) were analyzed. MONALEESA-3 is registered with ClinicalTrials.gov (NCT02422615).

RESULTS

At data cutoff (January 12, 2022; median follow-up time, 70.8 months), mOS was 67.6 versus 51.8 months with 1L ribociclib versus placebo (hazard ratio (HR) 0.67; 95% CI 0.50-0.90); 16.5% and 8.6% of ribociclib and placebo patients, respectively, were still receiving treatment. PFS2 (HR 0.64) and CFS (HR 0.62) favored ribociclib versus placebo. Among those who discontinued treatment, 16.7% and 35.0% on ribociclib or placebo, respectively, received a subsequent CDK4/6i. No new safety signals were observed.

CONCLUSIONS

This analysis of MONALEESA-3 reports the longest mOS thus far (67.6 months) for 1L patients in a phase III ABC trial. These results in a 1L population show that the OS benefit of ribociclib was maintained through extended follow-up, further supporting its use in HR+/HER2- ABC.

Comparative efficacy and safety of different combinations of three CDK4/6 inhibitors with endocrine therapies in HR+/HER-2 - metastatic or advanced breast cancer patients: a network meta-analysis

BACKGROUND

This network meta-analysis aimed to assess the comparative efficacy and safety of combinations involving three cyclin-dependent kinase 4/6 (CDK4/6) inhibitors and endocrine therapies (ETs) in patients with metastatic or advanced breast cancer (BC) who are hormone receptor-positive (HR+) and human epidermal growth factor receptor 2-negative (HER2-).

METHODS

We initially identified relevant studies from previous meta-analyses and then conducted a comprehensive search of PubMed, Embase, and the Cochrane Central Register of Controlled Trials (CENTRAL) databases to locate additional studies published between February 2020 and September 2021. Essential data were extracted, and a network meta-analysis was performed using R 4.1.1 software with a random-effects model. Furthermore, we assigned rankings to all available treatment combinations by calculating their cumulative probability.

RESULTS

Data analysis included ten reports from nine studies. Pooled results demonstrated that each treatment combination significantly reduced the hazard risk of progression-free survival (PFS) compared to treatment with an aromatase inhibitor (AI) or fulvestrant alone. However, there were no differences observed in PFS or overall survival (OS) among the different treatment combinations. Additionally, patients receiving palbociclib plus AI and abemaciclib plus AI or fulvestrant experienced more severe adverse events (AEs), with hazard ratios (HRs) of 10.83 (95% confidence interval [CI] = 2.3 to 52.51) and 4.8 (95%CI = 1.41 to 16.21), respectively. The HR for ribociclib plus AI was 9.45 (95%CI = 2.02 to 43.61), and the HR for palbociclib plus fulvestrant was 6.33 (95%CI = 1.03 to 39.86). Based on the ranking probabilities, palbociclib plus fulvestrant had the highest probability of achieving superior PFS (37.65%), followed by abemaciclib plus fulvestrant (28.76%). For OS, ribociclib plus fulvestrant ranked first (34.11%), with abemaciclib plus fulvestrant in second place (25.75%). In terms of safety, palbociclib plus AI (53.98%) or fulvestrant (51.37%) had the highest probabilities of being associated with adverse events.

CONCLUSIONS

Abemaciclib plus fulvestrant or ribociclib plus AI appear to be effective and relatively safe for the treatment of HR+/HER2- metastatic or advanced BC patients. However, given the reliance on limited evidence, our findings require further validation through additional studies.

CDK4/6 inhibitors, PI3K/mTOR inhibitors, and HDAC inhibitors as second-line treatments for hormone receptor-positive, HER2-negative advanced breast cancer: a network meta-analysis

BACKGROUND

This study sought to compare the benefits and safety of agents including Cyclin-dependent kinase 4/6 (CDK4/6) inhibitors, phosphoinositide 3-kinase (PI3K)/mammalian target of rapamycin (mTOR) inhibitors, and histone deacetylase (HDAC) inhibitors as second-line treatments for these patients by conducting a comprehensive systematic review and network meta-analysis.

METHODS

The Medline, Embase and Cochrane Library databases were searched for randomized trials comparing CDK4/6 inhibitors, PI3K/mTOR inhibitors, or HDAC inhibitors vs. placebo with the addition of exemestane or fulvestrant as second-line treatments in patients with HR + advanced breast cancer up to December 16, 2021. Outcomes of interest were progression-free survival (PFS), overall response rate (ORR), overall survival (OS), clinical benefit rate (CBR), and grade 3-4 adverse drug events (ADEs). The present study was conducted according to the Cochrane Collaboration and PRISMA statements. The overall effect was pooled using the random effects model.

RESULTS

Seventeen studies with a total of 9,100 participants were included in the current study. Compared with placebo plus fulvestrant, PFS was significantly improved by CDK4/6 inhibitor plus fulvestrant, mTOR inhibitor plus fulvestrant, mTOR inhibitor plus exemestane, and PI3K inhibitor plus fulvestrant, but not HDAC inhibitor plus exemestane. While mTOR inhibitor plus exemestane was the best regimen (SUCRA value 89.5%), the mTOR inhibitor plus exemestane regimen induced more severe adverse events (SAEs) than the HDAC inhibitor plus exemestane regimen [OR, 95% CI: 2.40 (1.40-4.10)].

CONCLUSION

mTOR inhibitor and CDK4/6 inhibitor-based regimens demonstrated superior clinical efficacy and comparable safety profiles as second-line treatment in patients with HR-positive, HER2-negative advanced breast cancer.

Recent advances in targeted strategies for triple-negative breast cancer

Triple-negative breast cancer (TNBC), a highly aggressive subtype of breast cancer, negatively expresses estrogen receptor, progesterone receptor, and the human epidermal growth factor receptor 2 (HER2). Although chemotherapy is the main form of treatment for patients with TNBC, the effectiveness of chemotherapy for TNBC is still limited. The search for more effective therapies is urgent. Multiple targeted therapeutic strategies have emerged according to the specific molecules and signaling pathways expressed in TNBC. These include PI3K/AKT/mTOR inhibitors, epidermal growth factor receptor inhibitors, Notch inhibitors, poly ADP-ribose polymerase inhibitors, and antibody-drug conjugates. Moreover, immune checkpoint inhibitors, for example, pembrolizumab, atezolizumab, and durvalumab, are widely explored in the clinic. We summarize recent advances in targeted therapy and immunotherapy in TNBC, with the aim of serving as a reference for the development of individualized treatment of patients with TNBC in the future.

Hormonal-Receptors-Positive and HER2-Negative Patients with Metastatic Breast Cancer Treated with First-Line Palbociclib and Hormonal Therapy: Impact of First-Cycle Neutropenia and Dose Reduction on Therapeutic Outcome

Background

CDK 4/6 inhibitors with hormonal therapy are the standard first-line therapy in metastatic hormonal receptors (HR)-positive and HER2-negative breast cancer. This study aims to assess the impact of neutropenia with 1st cycle, dose reduction, HER2-low status, and other clinicopathological factors on survival outcomes with the first-line palbociclib and hormonal therapy. Patients and Methods. In this retrospective study, we recruited patients with metastatic HR-positive and HER2-negative breast cancer. Neutropenia with 1st cycle, palbociclib dose reduction in addition to different clinicopathological and survival data were checked in patients' medical records. Survival outcomes were compared according to the abovementioned factors.

Results

We recruited 150 patients who received first-line palbociclib with hormonal therapy. 86% of patients developed 1st cycle neutropenia which was more common in patients with high Ki67. Dose reduction was recorded in 46.7% of patients and it was more common in patients with higher Allred scores (scores 7-8). The median progression-free survival (PFS) of the study group was 22 months. No significant difference was observed in PFS according to the 1st cycle of neutropenia or grade of neutropenia. Similarly, no difference in PFS according to palbociclib dose reduction and HER2 low status was observed. Only the Allred score and having a single site of metastasis had an independent significant relation with PFS. The median overall survival (OS) of the study group was 39 months. No significant difference was observed in OS according to the 1st cycle neutropenia, grade of neutropenia, palbociclib dose reduction, and HER2-low status. Only the Allred score and having a single site of metastasis had an independent significant relation with OS. In addition, no difference was observed in PFS and OS according to ECOG PS (2 vs. 0-1) or menopausal status.

Conclusion

No significant impact of the 1st cycle neutropenia, dose reduction, having ECOG PS2, menopausal status, or HER2 low status on survival outcome was observed. Survival outcome was significantly better in patients with single metastatic sites and higher ER-Allred scores.

SCR-6852, an oral and highly brain-penetrating estrogen receptor degrader (SERD), effectively shrinks tumors both in intracranial and subcutaneous ER + breast cancer models

BACKGROUND

Targeted estrogen receptor degradation has been approved to effectively treat ER + breast cancers. Due to the poor bioavailability of fulvestrant, the first generation of SERD, many efforts were made to develop oral SERDs. With the approval of Elacestrant, oral SERDs demonstrated superior efficacy than fulvestrant. However, due to the poor ability of known SERDs to penetrate the blood-brain barrier (BBB), breast cancer patients with brain metastasis cannot benefit from clinical SERDs.

METHODS

The ER inhibitory effects were evaluated on ERα protein degradation, and target genes downregulation. And anti-proliferation activities were further determined in a panel of ER + breast cancer cell lines. The subcutaneous and intracranial ER + tumor models were used to evaluate the efficacy of anti-tumor effects. Brain penetrability was determined in multiple animal species.

RESULTS

SCR-6852 is a novel SERD and currently is under early clinical evaluation. In vitro studies demonstrated that it strongly induced both wildtype and mutant ERα degradation. It potently inhibited cell proliferation in a panel of ER + breast cancer cell lines, including the cell lines containing ESR1 mutations (Y537 and D538). Furthermore, SCR-6852 exhibited pure antagonistic activities on the ERɑ signal axis identified both in vitro and in vivo. Oral administration of SCR-6852 at 10 mg/kg resulted in tumor shrinkage which was superior to Fulvestrant at 250 mg/kg, notably, in the intracranial tumor model, SCR-6852 effectively inhibited tumor growth and significantly prolonged mice survival, which correlated well with the high exposure in brains. In addition to mice, SCR-6852 also exhibited high brain penetrability in rats and dogs.

CONCLUSIONS

SCR-6852 is a novel SERD with high potency in inducing ERα protein degradation and pure antagonistic activity on ERɑ signaling in vitro and in vivo. Due to the high brain penetrability, SCR-6852 could be used to treat breast patients with brain metastasis.

Modeling the novel SERD elacestrant in cultured fulvestrant-refractory HR-positive breast circulating tumor cells

PURPOSE

Metastatic hormone receptor-positive (HR+) breast cancer initially responds to serial courses of endocrine therapy, but ultimately becomes refractory. Elacestrant, a new generation FDA-approved oral selective estrogen receptor degrader (SERD) and antagonist, has demonstrated efficacy in a subset of women with advanced HR+breast cancer, but there are few patient-derived models to characterize its effect in advanced cancers with diverse treatment histories and acquired mutations.

METHODS

We analyzed clinical outcomes with elacestrant, compared with endocrine therapy, among women who had previously been treated with a fulvestrant-containing regimen from the recent phase 3 EMERALD Study. We further modeled sensitivity to elacestrant, compared with the currently approved SERD, fulvestrant in patient-derived xenograft (PDX) models and cultured circulating tumor cells (CTCs).

RESULTS

Analysis of the subset of breast cancer patients enrolled in the EMERALD study who had previously received a fulvestrant-containing regimen indicates that they had better progression-free survival with elacestrant than with standard-of-care endocrine therapy, a finding that was independent estrogen receptor (ESR1) gene mutations. We modeled elacestrant responsiveness using patient-derived xenograft (PDX) models and in ex vivo cultured CTCs derived from patients with HR+breast cancer extensively treated with multiple endocrine therapies, including fulvestrant. Both CTCs and PDX models are refractory to fulvestrant but sensitive to elacestrant, independent of mutations in ESR1 and Phosphatidylinositol-4,5-Bisphosphate 3-Kinase Catalytic Subunit Alpha (PIK3CA) genes.

CONCLUSION

Elacestrant retains efficacy in breast cancer cells that have acquired resistance to currently available ER targeting therapies. Elacestrant may be an option for patients with HR+/HER2- breast cancer whose disease progressed on fulvestrant in the metastatic setting.

TRANSLATIONAL RELEVANCE

Serial endocrine therapy is the mainstay of management for metastatic HR+breast cancer, but acquisition of drug resistance highlights the need for better therapies. Elacestrant is a recently FDA-approved novel oral selective estrogen receptor degrader (SERD), with demonstrated efficacy in the EMERALD phase 3 clinical trial of refractory HR+breast cancer. Subgroup analysis of the EMERALD clinical trial identifies clinical benefit with elacestrant in patients who had received prior fulvestrant independent of the mutational status of the ESR1 gene, supporting its potential utility in treating refractory HR+breast cancer. Here, we use pre-clinical models, including ex vivo cultures of circulating tumor cells and patient-derived xenografts, to demonstrate the efficacy of elacestrant in breast cancer cells with acquired resistance to fulvestrant.

Real-world treatment patterns of subsequent therapy after palbociclib in patients with advanced breast cancer in Japan

PURPOSE

The optimal treatment following endocrine therapy (ET) plus a cyclin-dependent kinase 4/6 inhibitor (CDK4/6i) has not been established. We aimed to investigate treatment patterns and time to treatment failure (TTF) of subsequent therapy after palbociclib in a Japanese real-world setting.

METHDS

This retrospective observational study used de-identified data of patients with advanced breast cancer treated with palbociclib, using a nationwide claims database (April 2008 to June 2021). Measures included the type of subsequent therapies after palbociclib (endocrine-based therapy: ET alone, ET + CDK4/6i, and ET + mammalian target of rapamycin inhibitor [mTORi]; chemotherapy; chemotherapy + ET; and others) and their TTFs. The median TTF and 95% confidence interval (CI) were estimated using the Kaplan-Meier method.

RESULTS

Of 1170 patients treated with palbociclib, 224 and 235 received subsequent therapies after first- and second-line palbociclib treatment, respectively. Among them, 60.7% and 52.8% were treated with endocrine-based therapies as first subsequent therapy, including ET + CDK4/6i (31.2% and 29.8%, respectively). The median TTF (95% CI) of ET alone, ET + CDK4/6i, and ET + mTORi as first subsequent therapy after first-line palbociclib were 4.4 (2.8-13.7), 10.9 (6.5-15.6), and 6.1 (5.1-7.2) months, respectively. No apparent relationship between the treatment duration of prior ET + palbociclib and subsequent abemaciclib was observed.

CONCLUSION

This real-world study revealed that one-third of the patients received sequential CDK4/6i after ET + palbociclib, and treatment duration of ET + CDK4/6i following ET + palbociclib was the longest among the treatment options. Further data are awaited to determine whether ET + targeted therapy with CDK4/6i and mTORi provides acceptable treatment options following ET + palbociclib.

"Diagnostic and Prognostic Biomarkers of Luminal Breast Cancer: Where are We Now?"

Luminal breast cancers are hormone receptor (estrogen and/or progesterone) positive that are further divided into HER2-negative luminal A and HER2-positive luminal B subtypes. According to currently accepted convention, they represent the most common subtypes of breast cancer, accounting for approximately 70% of cases. Biomarkers play a critical role in the functional characterization, prognostication, and therapeutic prediction, rendering them indispensable for the clinical management of invasive breast cancer. Traditional biomarkers include clinicopathological parameters, which are increasingly extended by genetic and other molecular markers, enabling the comprehensive characterization of patients with luminal breast cancer. Liquid biopsies capturing and analyzing circulating tumor cells (CTCs) and circulating tumor DNA (ctDNA) are emerging technologies that envision personalized management through precision oncology. This article reviews key biomarkers in luminal breast cancer and ongoing developments.

CDK4/6 Inhibitor Resistance in Hormone Receptor-Positive Metastatic Breast Cancer: Translational Research, Clinical Trials, and Future Directions

The emergence of CDK4/6 inhibitors, such as palbociclib, ribociclib, and abemaciclib, has revolutionized the treatment landscape for hormone receptor-positive breast cancer. These agents have demonstrated significant clinical benefits in terms of both progression-free survival and overall survival. However, resistance to CDK4/6 inhibitors remains a challenge, limiting their long-term efficacy. Understanding the complex mechanisms driving resistance is crucial for the development of novel therapeutic strategies and the improvement of patient outcomes. Translational research efforts, such as preclinical models and biomarker studies, offer valuable insight into resistance mechanisms and may guide the identification of novel combination therapies. This review paper aims to outline the reported mechanisms underlying CDK4/6 inhibitor resistance, drawing insights from both clinical data and translational research in order to help direct the future of treatment for hormone receptor-positive metastatic breast cancer.

Oxidative phosphorylation is a metabolic vulnerability of endocrine therapy and palbociclib resistant metastatic breast cancers

Resistance to endocrine treatments and CDK4/6 inhibitors is considered a near-inevitability in most patients with estrogen receptor positive breast cancers (ER + BC). By genomic and metabolomics analyses of patients' tumours, metastasis-derived patient-derived xenografts (PDX) and isogenic cell lines we demonstrate that a fraction of metastatic ER + BC is highly reliant on oxidative phosphorylation (OXPHOS). Treatment by the OXPHOS inhibitor IACS-010759 strongly inhibits tumour growth in multiple endocrine and palbociclib resistant PDX. Mutations in the PIK3CA/AKT1 genes are significantly associated with response to IACS-010759. At the metabolic level, in vivo response to IACS-010759 is associated with decreased levels of metabolites of the glutathione, glycogen and pentose phosphate pathways in treated tumours. In vitro, endocrine and palbociclib resistant cells show increased OXPHOS dependency and increased ROS levels upon IACS-010759 treatment. Finally, in ER + BC patients, high expression of OXPHOS associated genes predict poor prognosis. In conclusion, these results identify OXPHOS as a promising target for treatment resistant ER + BC patients.

Epigenetic reprogramming of cell cycle genes by ACK1 promotes breast cancer resistance to CDK4/6 inhibitor

Hormone receptor-positive, HER2-negative advanced breast cancers exhibit high sensitivity to CDK4/6 inhibitors such as palbociclib. However, most patients inevitably develop resistance, thus identification of new actionable therapeutic targets to overcome the recurrent disease is an urgent need. Immunohistochemical studies of tissue microarray revealed increased activation of non-receptor tyrosine kinase, ACK1 (also known as TNK2) in most of the breast cancer subtypes, independent of their hormone receptor status. Chromatin immunoprecipitation studies demonstrated that the nuclear target of activated ACK1, pY88-H4 epigenetic marks, were deposited at cell cycle genes, CCNB1, CCNB2 and CDC20, which in turn initiated their efficient transcription. Pharmacological inhibition of ACK1 using its inhibitor, (R)-9b dampened CCNB1, CCNB2 and CDC20 expression, caused G2/M arrest, culminating in regression of palbociclib-resistant breast tumor growth. Further, (R)-9b suppressed expression of CXCR4 receptor, which resulted in significant impairment of metastasis of breast cancer cells to lung. Overall, our pre-clinical data identifies activated ACK1 as an oncogene that epigenetically controls the cell cycle genes governing the G2/M transition in breast cancer cells. ACK1 inhibitor, (R)-9b could be a novel therapeutic option for the breast cancer patients that have developed resistance to CDK4/6 inhibitors.

Interstitial lung disease and CDK4/6 inhibitors in the treatment of breast cancer

INTRODUCTION

CDK4/6 inhibitors have changed the treatment paradigm of many patients living with metastatic and early-stage high-risk hormone receptor (HR)-positive breast cancer. Even though patients and clinicians are aware and learning how to manage common adverse events, such as bone marrow suppression and gastrointestinal toxicities, there are less common and potentially severe adverse events, such as interstitial lung disease (ILD), that require special consideration.

AREAS COVERED

In this narrative review, we discuss the incidence, mechanism, and treatment of CDK4/6 inhibitor associated ILD.

EXPERT OPINION

CDK4/6 inhibitors in combination with endocrine therapy (ET) are standard treatment for HR-positive, HER2-negative metastatic breast cancer and for selected patients with early stage HR-positive breast cancer. Common toxicities of these medications are often controlled with dose reductions, dose interruptions, and/or prophylactic medications, such as antidiarrheals. However, there are a small subset of patients at risk for less common and potentially severe toxicities, such as ILD. Individualized risk should be considered, including underlying lung disease, thrombosis risk and drug-drug interactions, in order to counsel patients about the risk of ILD.

Is Palbociclib a cost-effective strategy in the second-line treatment of metastatic breast cancer in Iran?

BACKGROUND & AIMS

This study evaluates the cost-effectiveness of Palbociclib in the second-line treatment of hormone receptor-positive (HR+) human epidermal growth factor receptor 2-negative (HER2-) metastatic breast cancer (MBC) in Iran.

METHODS

The present economic evaluation used a partitioned survival model (PSM). This model compares lifetime costs and disease outcomes among groups receiving different medication combinations containing Palbociclib, Fulvestrant, Everolimus, Ribociclib, and Abemaciclib as the second-line therapy for HR+/HER2- MBC. The model was conducted from Iran's healthcare perspective, structured with 1-month cycles, and the evaluation time horizon in the base analysis was set to 180 cycles (15 years). Transition probabilities were extracted using the survival curves. The cost information was extracted based on the year 2020. The Quality Adjusted Life Years (QALY) was considered the final outcome unit, and the cost-effectiveness of different combinations is calculated as cost per QALY. The annual discount rate of 5% was considered for costs and QALYs. Two times Iran's GDP per capita (800,000,000 IRR = US$5934) was used as the threshold. Finally, due to the uncertainty of some parameters, deterministic and probabilistic sensitivity analyses were carried out.

RESULTS

The base case results showed that the highest cost was for the 'Ribociclib+ Fulvestrant' combination (US$89,629.56), and the lowest price was for the 'Iranian Everolimus + Fulvestrant' combination (US$10,740.09). 'Palbociclib + Fulvestrant' brings about the highest value of 1.456 incremental QALYs compared to other strategies. Finally, the 'Iranian Palbociclib + Fulvestrant' was the cost-effective combination, with an incremental cost-effectiveness ratio (ICER) of US$4,201 compared to other strategies. The base case results were supported by the probabilistic sensitivity analysis. Deterministic sensitivity analysis showed that the cost of Iranian Palbociclib has a threshold of US$582.99.

CONCLUSIONS

The 'Iranian Palbociclib + Fulvestrant' combination was cost-effective in second-line therapy for HR+ HER2- MBC in Iran.

Real-world outcomes of patients with metastatic endocrine-responsive breast cancer receiving palbociclib-based combinations

Aim: To describe treatment journey and clinical outcomes after palbociclib initiation in HR+/HER2- breast cancer patients across multiple lines. Materials & methods: Adult patients (n = 559) were identified in a population-based study between January 2018 and June 2020. Results: Median follow-up time was 41.2 months. The starting dose was 125 mg for more than 85% of patients, and a third had dose reduction. Median time on treatment was 30.5 months for palbociclib + aromatase inhibitors for patients that received first-line treatment after metastatic diagnosis, and 12.6 months for palbociclib + fulvestrant across multiple lines, and longer for patients that had a dose reduction during treatment. At 48 months, 59.3 and 27.3% of patients were still alive, respectively. Subsequent lines resulted in median time on treatment of 4.4-7.7 months in both groups. Conclusion: Time on treatment for palbociclib was comparable to data from clinical trials, and follow-up allowed us to examine subsequent treatment after initial treatment failure. Dose reduction was common in the real-world setting and did not adversely affect efficacy.

A comprehensive update of hormone-related pharmacokinetic variations associated with breast cancer drugs

INTRODUCTION

Drugs available for the treatment of breast cancer are increasing, yielding improved oncological outcomes. The efficacy and safety of anticancer drugs significantly depend on pharmacokinetic profiles, which could be influenced by several factors, such as sex hormones.

AREAS COVERED

This article discusses the potential hormone-related pharmacokinetic influences on novel breast cancer pharmacotherapies.

EXPERT OPINION

Recently approved drugs for the treatment of breast cancer belong to different classes, each with unique pharmacokinetic profile. The impact of hormones, such as estrogen and progesterone, may occur at different steps of drug metabolism. Key effects of sex hormones ha ve been reported on multidrug-resistant transporters and enzymes involved in the liver metabolism of drugs, such as cytochromes. Nevertheless, no data is currently available to establish hormone-related metabolic interactions that may account for variability in drug scheduling and selection. Whereas we recognize influences may occur, we do not assume hormones alone can yield clinically significant metabolic changes. Rather, we believe that hormonal influences should be considered along with other elements that may affect drugs metabolism, such as concomitant medications, age-related pharmacokinetic changes, and genetic polymorphisms, in order to deliver treatment personalization and ensure better tolerability and safety of anticancer treatments.

Incorporating clinicopathological and molecular risk prediction tools to improve outcomes in early HR+/HER2- breast cancer

Stratification of recurrence risk is a cornerstone of early breast cancer diagnosis that informs a patient's optimal treatment pathway. Several tools exist that combine clinicopathological and molecular information, including multigene assays, which can estimate risk of recurrence and quantify the potential benefit of different adjuvant treatment modalities. While the tools endorsed by treatment guidelines are supported by level I and II evidence and provide similar prognostic accuracy at the population level, they can yield discordant risk prediction at the individual patient level. This review examines the evidence for these tools in clinical practice and offers a perspective of potential future risk stratification strategies. Experience from clinical trials with cyclin D kinase 4/6 (CDK4/6) inhibitors in the setting of hormone receptor-positive (HR+)/human epidermal growth factor receptor 2-negative (HER2-) early breast cancer is provided as an illustrative example of risk stratification.

A Potential Anti-Glioblastoma Compound LH20 Induces Apoptosis and Arrest of Human Glioblastoma Cells via CDK4/6 Inhibition

Glioblastoma (GBM) is a deadly brain tumor characterized by signaling dysregulation and aberrant cell cycle control. The CDK4/6-Rb axis is dysregulated in approximately 80% of all GBM cases. In this study, the anti-GBM effect of a novel pyrimidin-2-amine, LH20 was evaluated in vitro using the primary GBM cell lines U87MG and U251. GBM cells were administered LH20 at concentrations of 0.1, 1, 4, 8, 10, 20, 100, and 200 µM for 24 and 48 h, and the proliferation rate was evaluated using a CCK8 assay. Migration, apoptosis, and cell cycle were also assessed using a wound healing assay, Annexin V-FITC/PI apoptosis assay, and cell cycle staining, respectively. The targets of LH20 were predicted using SwissTargetPrediction and molecular docking. Western blotting analysis was performed to confirm the anti-GBM mechanism of LH20. We found that at concentrations of 4, 8, and 10 µM, LH20 significantly inhibited the proliferation and migration of U87MG and U251 cells, induced late phase apoptosis, promoted tumor cell necrosis, and arrested the G2/M phase of the cell cycle. LH20 also inhibited CDK4 and CDK6 activities by decreasing the phosphorylation of Rb. Our results suggest LH20 as a potential treatment strategy against GBM.

Microneedle Patch Delivery of PROTACs for Anti-Cancer Therapy

Proteolysis-targeting chimera (PROTAC) is an emerging technique for degrading disease-related proteins. However, the current PROTACs suffer from inadequate solubility and lack of organ targeting, which has hampered their druggability. Herein, we report direct and sustained delivery of PROTACs using microneedle patches to the diseased tissues. In this study, we use an estrogen receptor alpha (ERα)-degrading PROTAC, ERD308, to treat ER-positive breast cancer. A pH-sensitive micelle, MPEG-poly(β-amino ester) (MPEG-PAE), is used to encapsulate ERD308 along with an FDA-approved CDK4/6 inhibitor, Palbociclib (Pal), before loading into biodegradable microneedle patches. These patches enable prolonged drug release into deep tumors, maintaining therapeutic levels for at least 4 days, with an excellent drug retention rate of over 87% in tumors. ERD308 released from the microneedle patches can sufficiently degrade ERα in MCF7 cells. Co-administration of ERD308 and Palbociclib exhibits excellent efficacy by over 80% tumor reduction as well as a good safety profile. Our work demonstrates the feasibility and proof-of-concept therapeutic potential of using microneedle patches to directly deliver PROTACs into tumors.

Capecitabine efficacy after cycline-dependent-kinase 4/6 inhibitor plus endocrine therapy in metastatic hormone receptor-positive breast cancer

BACKGROUND

The combination of endocrine treatment with cycline-dependent-kinase 4/6 inhibitor is the new standard of treatment in hormone receptor-positive HER2 negative metastatic breast cancer. The optimal subsequent treatment after CDK4/6 inhibitor remain unclear. As recommended by standard guidelines, capecitabine, an oral chemotherapy is a therapeutic option in endocrine resistant metastatic breast cancer. The objective of this study was to evaluate capecitabine efficacy after disease progression under combination of ET and CDK4/6 inhibitor in a hormone receptor positive metastatic breast cancer population.

PATIENTS AND METHODS

Patients progressing under CDK 4/6 inhibitor plus ET and treated with capecitabine, between January 2016 and December 2020, were retrospectively included. Primary endpoint was time to treatment failure (TTF) on capecitabine. Logistic regression were used to identify predictive factors: exclusive bone versus visceral metastases, first-line versus ≥ 2 lines of combination therapy, aromatase inhibitor (AI) versus fulvestrant.

RESULTS

Fifty-six patients with a 62-year median age (IC95% 42-81) were analyzed. The CDK 4/6 inhibitor and ET combination was prescribed in first-line setting in 26 patients (46%). Twenty-five patients (44%) had exclusive bone metastasis. Median TTF was 6.1 months. Six patients discontinued capecitabine due to toxicity. Outcomes were not significantly different regardless of metastases localization, ET, and treatment line of the combination of CDK 4/6 inhibitor and ET. Median PFS was 7.1 months. Median OS was 41.3 months.

CONCLUSION

Compared to other data of capecitabine prescribed in patients with hormonal resistant MBC, this retrospective study suggests that capecitabine remains effective after CDK 4/6 inhibitor plus ET progression, regardless of therapeutic-line setting and metastases localization.

MICRO ABSTRACT

Cycline dependant kinase 4/6 inhibitor plus endocrine therapy have become the standard of care in metastatic hormone receptor positive (HR+) breast cancer (BC). Few data reported the optimal subsequent therapy after progression under the combination. Capecitabine is a therapeutic option in endocrine resistant HR+/HER2- metastatic breast cancer. Data evaluating efficacy of capecitabine after disease progression on endocrine therapy plus cycline-dependant kinase 4/6 inhibitor are poor. This study showed a 6.1-month median time to treatment failure on capecitabine. Capecitabine remained effective regardless of therapeutic-line setting and metastases localization.

Efficacy and clinical outcome of chemotherapy and endocrine therapy as first-line treatment in patients with hormone receptor-positive HER2-negative metastatic breast cancer

BACKGROUND

Endocrine therapy (ET) and ET-based regimens are the preferred first-line treatment options for hormone receptor (HR)-positive and human epidermal growth factor receptor 2 (HER2)-negative metastatic breast cancer (HR+/HER2- MBC), while chemotherapy (CT) is commonly used in clinical practice. The aim of this study was to investigate the efficacy and clinical outcome of ET and CT as first-line treatment in Chinese patients with HR+/HER2- MBC.

METHODS

Patients diagnosed with HR+/HER2-MBC between January 1st, 1996 and September 30th, 2018 were screened from the Chinese Society of Clinical Oncology Breast Cancer database. The initial and maintenance first-line treatment, progression-free survival (PFS), and overall survival (OS) were analyzed.

RESULTS

Among the 1877 included patients, 1215 (64.7%) received CT and 662 (35.3%) received ET as initial first-line treatment. There were no statistically significant differences in PFS and OS between patients receiving ET and CT as initial first-line treatment in the total population (PFS: 12.0 vs. 11.0 months, P = 0.22; OS: 54.0 vs . 49.0 months, P =0.09) and propensity score matched population. For patients without disease progression after at least 3 months of initial therapy, maintenance ET following initial CT (CT-ET cohort, n = 449) and continuous schedule of ET (ET cohort, n = 527) had longer PFS than continuous schedule of CT (CT cohort, n = 406) in the total population (CT-ET cohort vs. CT cohort: 17.0 vs . 8.5 months; P <0.01; ET cohort vs . CT cohort: 14.0 vs . 8.5 months; P <0.01) and propensity score matched population. OS in the three cohorts yielded the same results as PFS.

CONCLUSIONS

ET was associated with similar clinical outcome to CT as initial first-line treatment. For patients without disease progression after initial CT, switching to maintenance ET showed superiority in clinical outcome over continuous schedule of CT.

The effect of low HER2 expression on treatment outcomes in metastatic hormone receptor positive breast cancer patients treated with a combination of a CDK4/6 inhibitor and endocrine therapy: A multicentric retrospective study

BACKGROUND

CDK4/6 inhibitors combined with endocrine therapy have significantly improved treatment outcomes for metastatic hormone receptor-positive (HR+) breast cancer patients. However, the impact of low HER2 expression on treatment response and progression-free survival (PFS) remains unclear.

METHODS

This multicenter retrospective study included 204 HR+ breast cancer patients treated with a combination of CDK4/6 inhibitor and endocrine therapy. HER2-zero disease was detected in 138 (68%) and HER2-low disease in 66 (32%) patients. Treatment-related characteristics and clinical outcomes were analyzed, with a median follow-up of 22 months.

RESULTS

The objective response rate (ORR) was 72.7% in the HER2 low group and 66.6% in the HER2 zero group (p = 0.54). Median PFS was not significantly different between the HER2-low and HER2 zero groups (19 months vs.18 months, p = 0.89), although there was a trend toward longer PFS in the HER2-low group for first-line treatment (24 months progression-free survival rate 63% vs 49%). In recurrent disease, the median PFS was 25 months in the HER2-low group and 12 months in the HER2-zero group (p = 0.08), while in de novo metastatic disease, the median PFS was 18 months in the HER2-low group and 27 months in the HER2-zero group (p = 0.16). The order of CDK4/6 inhibitor use and the presence of visceral metastasis were identified as independent variables affecting PFS.

CONCLUSION

Low HER2 expression did not significantly impact treatment response or PFS in HR+ breast cancer patients treated with a CDK4/6 inhibitor and endocrine therapy. Because of the conflicting results in the literature, further prospective studies are needed to evaluate the clinical significance of HER2 expression in HR+ breast cancer.