Cyclin-dependent kinase 4/6 inhibitors in hormone receptor-positive early breast cancer: preliminary results and ongoing studies

The cyclin D-cyclin-dependent kinase (CDK) 4/6-inhibitors (CDK4/6i) induce cell cycle arrest in the G1 phase what eventually can prevent the proliferation of cancer cells. The CDK4/6i have changed the landscape of treatment options for ER-positive, HER2-negative metastatic breast cancer. Currently, palbociclib, ribociclib, and abemaciclib are approved by the US Food and Drug Administration in this setting. This success encouraged the researchers to examine CDK4/6i activity in (neo)adjuvant setting. In this review, clinical data to date and ongoing clinical trials with palbociclib, ribociclib, and abemaciclib in the early breast cancer are discussed. A literature search of these topics was carried out using PubMed and data reported at international oncology meetings and clinicaltrials.gov were included. Currently, we have the early promising data from Phase II clinical trials of CDK4/6i efficacy in the neoadjuvant setting in women with HR-positive breast cancer. Moreover, there are numerous studies that are in progress today in (neo)adjuvant setting.     

Racial disparities in neutrophil counts among patients with metastatic breast cancer during treatment with CDK4/6 inhibitors

Breast Cancer Research and Treatment - The three CDK4/6 inhibitors (CDK4/6i) approved for use in HR-positive/HER2-negative metastatic breast cancer (MBC), palbociclib, ribociclib, and abemaciclib,...     

Limited clinical activity of palbociclib and ribociclib monotherapy in advanced cancers with cyclin D-CDK4/6 pathway alterations in the Dutch DRUP and Australian MoST trials

The Dutch Drug Rediscovery Protocol (DRUP) and the Australian Cancer Molecular Screening and Therapeutic (MoST) Program are similar nonrandomized, multidrug, pan-cancer trial platforms that aim to identify signals of clinical activity of molecularly matched targeted therapies or immunotherapies outside their approved indications. Here, we report results for advanced or metastatic cancer patients with tumors harboring cyclin D-CDK4/6 pathway alterations treated with CDK4/6 inhibitors palbociclib or ribociclib. We included adult patients that had therapy-refractory solid malignancies with the following alterations: amplifications of CDK4, CDK6, CCND1, CCND2 or CCND3, or complete loss of CDKN2A or SMARCA4. Within MoST, all patients were treated with palbociclib, whereas in DRUP, palbociclib and ribociclib were assigned to different cohorts (defined by tumor type and alteration). The primary endpoint for this combined analysis was clinical benefit, defined as confirmed objective response or stable disease ≥16 weeks. We treated 139 patients with a broad variety of tumor types; 116 with palbociclib and 23 with ribociclib. In 112 evaluable patients, the objective response rate was 0% and clinical benefit rate at 16 weeks was 15%. Median progression-free survival was 4 months (95% CI: 3-5 months), and median overall survival 5 months (95% CI: 4-6 months). In conclusion, only limited clinical activity of palbociclib and ribociclib monotherapy in patients with pretreated cancers harboring cyclin D-CDK4/6 pathway alterations was observed. Our findings indicate that monotherapy use of palbociclib or ribociclib is not recommended and that merging data of two similar precision oncology trials is feasible.     

CDK4/6 inhibition in early and metastatic breast cancer: A review

Breast cancer (BC) is responsible for 14% of cancer-related deaths in women [1]. Cyclin-dependent kinase (CDK) 4/6 inhibitors are a new class of selective drugs, offering an effective and tolerable treatment. CDK4/6 inhibitors induce cell cycle arrest in the G1 phase, and may thereby prevent tumour progression. Three CDK4/6 inhibitors have been tested in clinical BC trials: palbociclib, ribociclib, and abemaciclib. The Food and Drug Administration (FDA) and European Commission (EMA) have approved palbociclib for the treatment of patients HR+ HER2- locally advanced or metastatic BC (aBC) in combination with an aromatase inhibitor as initial therapy in postmenopausal women or in combination with fulvestrant in women who have received prior endocrine therapy. Ribociclib has been approved by the FDA in combination with an aromatase inhibitor as initial therapy for postmenopausal women with HR+ HER2- aBC. Moreover, CDK4/6 inhibitors have shown promising results in the (neo)adjuvant setting. In this review, the principal completed and ongoing clinical trials in aBC are reviewed for both the metastatic as (neo)adjuvant setting. Tables will provide a complete overview of the ongoing clinical trials. At last, the future perspectives of these CDK4/6 inhibitors are discussed.     

Comparison of treatment-related adverse events of different Cyclin-dependent kinase 4/6 inhibitors in metastatic breast cancer: A network meta-analysis

BackgroundPalbociclib, ribociclib and abemaciclib have all been approved in combination with endocrine therapy in hormone-receptor positive, HER2 negative metastatic breast cancer. While the efficacy of these drugs appears similar, differences in safety and tolerability are apparent.MethodsWe searched PubMed and ASCO, ESMO and SABCS proceedings to identify randomized trials of palbociclib, ribociclib and abemaciclib. Data on common and serious adverse events (AE) were extracted for each approved drug. The odds ratio for each AE and the hazard ratio for progression-free survival were calculated relative to endocrine therapy alone. A network meta-analysis was then performed for each endocrine therapy backbone (aromatase inhibitor (AI) or fulvestrant) to compare ribociclib and abemaciclib to palbociclib.Results8 trials were included in the analysis and comprised 2799 patients receiving cyclin-dependent kinase 4/6 inhibitors palbociclib: 873 patients; ribociclib: 1153 patients; abemaciclib: 773 patients. In 5 trials (1524 patients), the endocrine therapy backbone was an AI and in 3 trials (1275 patients) it was fulvestrant. Compared to palbociclib, ribociclib and abemaciclib showed significantly lower grade 3–4 neutropenia, but significantly higher GI toxicity. Treatment discontinuation was higher with abemaciclib than other drugs. Efficacy of the 3 drugs was similar. Compared to palbociclib, for AI backbone, the HR for PFS for ribociclib was 0.98 and for abemaciclib 1.02. For fulvestrant backbone, the HR were 0.88 and 0.93 respectively.ConclusionsPalbociclib, ribociclib and abemaciclib have comparable efficacy, but differences in safety and tolerability. Abemaciclib has worse tolerability with significantly higher treatment discontinuation likely due to GI toxicity.     

Palbociclib or Ribociclib in First-Line Treatment in Patients With Hormone Receptor–Positive/Human Epidermal Receptor 2–Negative Advanced or Metastatic Breast Cancer? A Perspective Based on Pharmacologic Costs

PurposeTo assess the pharmacologic costs of CDK4/6 inhibitors (palbociclib and ribociclib) in hormone receptor–positive (HR⁺)/human epidermal receptor 2–negative (HER2^?) advanced or metastatic breast cancer (BC). Pivotal phase 3 randomized controlled trials (RCTs) were considered.DiscussionTwo phase 3 RCTs including 1334 patients were considered. European Society for Medical Oncology Magnitude of Clinical Benefit Scale reached grade 3 for the PALOMA-2 and MONALEESA-2 trials. Pharmacologic costs of palbociclib and ribociclib at full dose were similar, at €3864 and €4002 per month of progression-free survival (PFS) gained, respectively. The reduction of dose of ribociclib (36.1% in the pivotal RCT vs. 36.0% of palbociclib in pivotal RCT) resulted in €2718 and €1348 per month of PFS gained at 400 and 200 mg daily, respectively.ConclusionWhen pharmacologic costs of drugs are combined with the measure of efficacy represented by PFS, both palbociclib and ribociclib are cost-effective first-line treatments in postmenopausal women with HR⁺/HER2^? advanced or metastatic BC, with a lower cost in favor of ribociclib in patients with dose reduction.     

Ribociclib for the treatment of hormone receptor-positive,human epidermal growth factor receptor 2-negative advanced breast cancer

Introduction: The emergence of cyclin-dependent kinases 4 and 6 (CDK4/6) inhibitors marked a significant advancement in the treatment of advanced breast cancer. Ribociclib is an orally bioavailable, highly selective inhibitor of CDK4/6. In combination with various endocrine therapies, ribociclib has demonstrated clinical activity as a first-line therapy for patients with HR+, HER2? advanced breast cancer, without compromising the favorable toxicity profile associated with endocrine therapy. Thus, ribociclib is now considered a new standard of care for HR+, HER2? advanced breast cancer.

Areas covered: This review provides a concise overview of the preclinical and clinical development of ribociclib, including evidence of its clinical activity and safety profile when combined with endocrine therapy in HR+, HER2? advanced breast cancer.

Expert commentary: CDK4/6 inhibition represents a promising treatment option for patients with HR+ metastatic breast cancer. Ribociclib significantly improved progression-free survival in patients receiving first-line endocrine therapy for HR+, HER2? advanced breast cancer. Planned and ongoing trials investigating ribociclib in combination with other endocrine therapies and in various clinical settings will help to determine the optimal treatment sequence for different patient populations.     

Molecular mechanisms of resistance to CDK4/6 inhibitors in breast cancer: A review

Deregulation of the cyclin D-CDK4/6-INK4-RB pathway leading to uncontrolled cell proliferation, is frequently observed in breast cancer. Currently, three selective CDK4/6 inhibitors have been FDA approved: palbociclib, ribociclib and abemaciclib. Despite promising clinical outcomes, intrinsic or acquired resistance to CDK4/6 inhibitors has limited the success of these treatments; therefore, the development of various strategies to overcome this resistance is of great importance. We highlight the various mechanisms that are directly or indirectly responsible for resistance to CDK4/6 inhibitors, categorizing them into two broad groups; cell cycle-specific mechanisms and cell cycle-nonspecific mechanisms. Elucidation of the diverse mechanisms through which resistance to CDK4/6 inhibitors occurs, may aid in the design of novel therapeutic strategies to improve patient outcomes. This review summarizes the currently available knowledge regarding mechanisms of resistance to CDK4/6 inhibitors, and possible therapeutic strategies that may overcome this resistance as well.     

Mechanisms of therapeutic CDK4/6 inhibition in breast cancer

Cyclin dependent kinase (CDK) 4/6 inhibitors have advanced the treatment of metastatic breast cancer by targeting the cell cycle machinery, interrupting intracellular and mitogenic hormone signals that stimulate proliferation of malignant cells. Preclinical evidence demonstrated that derangements of cyclin D1, CDK4/6, and retinoblastoma expression are common in breast cancer, and suggested a therapeutic benefit from interrupting this axis required for cell cycle progression. Studies of cell lines and animal models of breast cancer have demonstrated the complex interplay between the cell cycle and estrogen receptor and human epidermal growth receptor 2 signaling, which informs our understanding of synergistic use of CDK4/6 inhibitors with endocrine therapy, as well as mechanisms of resistance to endocrine therapy. Interestingly, estrogen receptor activity leads to upregulation of cyclin D1 expression, but the estrogen receptor is also in turn activated by cyclin D1, independent of estrogen binding. Early CDK inhibitors were nonspecific and limited by systemic toxicities, while the current generation of CDK4/6 inhibitors have shown promise in the treatment of hormone receptor-positive breast cancer. Preclinical investigations of the three CDK4/6 inhibitors approved by the US Food and Drug Administration (palbociclib, ribociclib, and abemaciclib) lend further insight into their mechanism of action, which will hopefully inform the future use and refinement of these therapies. Finally, we summarize evidence for additional novel CDK4/6 inhibitors currently in development.     

CDK4/6 Inhibition as a therapeutic strategy in breast cancer: palbociclib,ribociclib, and abemaciclib

With 40,920 American women expected to die from breast cancer in 2018 and global health estimates that more than 508,000 women died in 2011 from this disease, the identification of novel therapeutic strategies for the treatment of breast cancer cannot be ignored. A breakthrough class of cancer drugs that has emerged in recent years and has had an impact in the treatment of breast cancer are the cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors, with palbociclib the first in class to have received regulatory approval for breast cancer. In this article we will compare and contrast three CDK4/6 inhibitors - palbociclib, ribociclib and abemaciclib - that have received regulatory approval for the treatment of metastatic breast cancer. Ribociclib and abemaciclib developed after the success of palbociclib represent examples of "me-too" therapies increasingly being deployed in oncology.     

Clinical development of CDK4/6 inhibitor for breast cancer

Endocrine therapy is the mainstay of treatment for patients with estrogen receptor positive (ER+)/HER2-negative (HER2?) metastatic breast cancer (MBC). Many clinicians consider the sequential endocrine therapy is gold standard strategy because of better outcome and the maintenance of a better quality of life (QOL) for MBC patients. However, clinical practice shall be changed according to development of CDK4/6 inhibitor in current. CDK4/6 is key kinase which promote the cell cycle, and especially the expression of cyclin D1 and the activation of CDK4/6 to drive breast cancer proliferation. Currently positive data of several clinical trials using three CDK4/6 inhibitors (palbocilcib, ribociclib, abemaciclib) were published and primary endpoint were met in all phase III studies. Therefore, practice change of endocrine therapy has been achieved in ER positive MBC. This review will present clinical trial data, including both the efficacy and safety of CDK4/6 inhibitors for MBC, and describe the designs of the mainly ongoing clinical trials examining CDK4/6 inhibitors for the treatment of MBC and EBC.     

Cyclin-dependent kinase 4/6 inhibitors as first-line treatment for post-menopausal metastatic hormone receptor-positive breast cancer patients: a systematic review and meta-analysis of phase III randomized clinical trials

Background

To compare the efficacy and toxicity of the combination of cyclin-dependent kinase 4/6 (CDK 4/6) inhibitors and nonsteroidal aromatase inhibitors (AI) versus AI alone as first-line therapy for patients with advanced hormone receptor-positive breast cancer.

Materials and methods

Phase III randomized clinical trials (RCT) were identified after a systematic review of electronic databases. A random-effect model was used to determine the pooled hazard ratio (HR) for progression-free survival (PFS) using the inverse-variance method. The Mantel–Haenszel method was used to calculate the pooled odds ratio (OR) for overall response, clinical benefit rate and treatment-related side effects. Heterogeneity was measured using the tau-squared and I² statistics.

Results

After a systematic search, three phase III RCT (n = 1827) were included. The use of CDK 4/6 inhibitors (abemaciclib, palbociclib, and ribociclib) in combination with an AI was significantly associated with longer PFS compared to the use of letrozole or anastrozole alone (HR: 0.57; 95% CI 0.50–0.65; p < 0.00001), with no significant heterogeneity among trials. Similarly, overall response rate and clinical benefit rate were higher for patients who received the combination therapy than for patients allocated to AI alone. Grade 3 or higher treatment-related side effects were more frequently reported for patients who received CDK 4/6 inhibitors (OR: 7.51; 95% CI 6.01–9.38; p < 0.00001), these included mainly neutropenia, leukopenia and anemia.

Conclusion

The addition of CDK 4/6 inhibitors (either abemaciclib, palbociclib, or ribociclib) to an AI (anastrozole or letrozole) significantly improved PFS, overall response rate, and clinical benefit rate in comparison with a nonsteroidal AI alone.

     

Optimal vascular access strategies for patients receiving chemotherapy for early-stage breast cancer: a systematic review

Purpose

Prospective information regarding the tolerability and efficacy of endocrine therapy (ET) alone and in combination with targeted agents in older patients in the metastatic setting is limited. This review summarizes available trial data in this population.

Methods

We searched PubMed for Phase 2 or 3 trials with age-stratified patient cohorts (≥ 65 vs. < 65 years in most studies) with hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2?) advanced breast cancer treated with ET ± targeted agents.

Results

We identified 19 studies reporting 10 clinical trials. Efficacy was similar in age-stratified subsets. There was a reduced disease progression risk for ET + everolimus, palbociclib, or ribociclib versus ET alone. In the first-line setting, median progression-free survival (mPFS) in older patients was 8.5, 26.2 months, and not reached with letrozole + temsirolimus, palbociclib, and ribociclib, respectively, and in younger patients was 9.0, 18.8 months, and not reached, respectively. In the second-line setting, older patients had mPFS of 6.8 and 9.9 months with everolimus + exemestane and palbociclib + fulvestrant, respectively, and younger patients had mPFS of 8.1 and 9.5 months, respectively. Tolerability was worse for combination therapy versus monotherapy. No age-related differences in discontinuations were observed for CDK4/6 inhibitors, although a higher rate of treatment discontinuation was observed for patients ≥ 70 years receiving everolimus + exemestane. Adverse event rates were similar in age-stratified subsets.

Conclusions

ET + CDK4/6 or mTOR inhibitors are likely safe and effective in older patients with HR+, HER2? advanced breast cancer.

     

Use of cyclin-dependent kinase (CDK) 4/6 inhibitors for hormone receptor-positive,human epidermal growth factor receptor 2-negative,metastatic breast cancer: a roundtable discussion by The Breast Cancer Therapy Expert Group (BCTEG)

Purpose

To provide an overview of clinical data supporting the use of cyclin-dependent kinases 4 and 6 (CDK 4/6) inhibitors in the treatment of hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2?), metastatic breast cancer (mBC), from the perspective of the practicing oncologist community.

Methods

A recent roundtable discussion was convened by The Breast Cancer Therapy Expert Group (BCTEG) to review existing data on this topic and its impact on their current practice.

Results

Level 1 evidence now supports use of a CDK 4/6 inhibitor in combination with endocrine therapy for patients with HR+, HER2?, mBC. Currently, there are no biomarkers that reliably define patients who will, or will not, benefit from the addition of a CDK 4/6 inhibitor to their endocrine therapy. Additional research is needed to identify the optimal sequencing of CDK 4/6 inhibitors in relation to other therapies as well as the optimal duration of therapy; at present, evidence suggests that use in the upfront setting is better than waiting for a later line of therapy, or adding after endocrine therapy has started.

Conclusions

Thus far, three CDK 4/6 inhibitors—palbociclib, ribociclib, and more recently, abemaciclib—have been approved for use in the setting of HR+, HER2?, mBC.  The degrees to which these agents differ in terms of CDK4/6 affinity, side-effect profiles, dosing, degree of central nervous system (CNS) penetration, optimal use in combination with antiestrogen therapy, and across other subsets of breast cancer, remain an active area of investigation.

     

Ribociclib-Induced Erythema Dyschromicum Perstans (Ashy Dermatosis)–Like Pigmentation in a Metastatic Breast Cancer Patient

Ribociclib is a selective cyclin-dependent kinase (CDK) 4/6 inhibitor that has been approved in combination with endocrine therapy for the treatment of hormone receptor-positive/human epidermal growth factor 2-negative advanced or metastatic breast cancer. The main dermatological adverse events associated with CDK 4/6 inhibitors that are described in the literature include skin rash, an increased risk of alopecia, and stomatitis. Erythema dyschromicum perstans (EDP), also known as ashy dermatosis, is characterized by acquired small and large slate-gray hyperpigmented macules with erythematous borders. There are currently no published reports of EDP-like or pigmentary changes induced by CDK 4/6 inhibitors. This report describes the first case of EDP-like pigmentation associated with ribociclib therapy.     

Polyclonal RB1 mutations and acquired resistance to CDK 4/6 inhibitors in patients with metastatic breast cancer

BackgroundWhile deregulation of the cyclin D1-CDK4/6-retinoblastoma pathway is common in hormone receptor positive (HR+) breast cancer, Rb is usually intact in HR+ breast cancer, and targeted CDK 4/6 inhibitors that act upstream of Rb, are routinely being utilized in clinical practice. However, factors that can lead to clinical resistance to CDK 4/6 inhibitors are not known.Patients and methodsWe identified patients who had pre- and post-genotyping in tissue and peripheral blood samples after receiving CDK 4/6 inhibitors. Genotyping was carried out in tumor tissue or blood collected before start of CDK 4/6 inhibitor and after disease progression on CDK 4/6 inhibitor, covering more than 90% of the coding region in RB1.ResultsWe identified detectable acquired RB1 mutations in circulating tumor DNA (ctDNA) after exposure to CDK4/6 inhibitor (palbociclib, palbociclib, ribociclib) for 5, 8, and 13 months, respectively, in three patients. The RB1 mutations included substitution in donor splicing site of exon 8 of the RB1 gene in patient #1; substitution in donor splicing site of exon 22 of RB1 gene, exon 19 deletion, exon 3 insertion in patient #2; and RB1 exon 16 H483Y mutation in patient #3. None of these RB1 mutations were present in the pre-CDK 4/6 specimen highlighting these molecular alterations, which lead to functional loss of Rb1, likely emerged under selective pressure from the CDK4/6 inhibitor potentially confering therapeutic resistance.ConclusionThis is the first clinical report to describe the emergence of somatic RB1 mutations after exposure to palbociclib or ribociclib, in patients with metastatic breast cancer. Further research is needed to validate these findings, identify how these mutations temporally emerge under selective pressure of CDK 4/6 inhibitor, and develop rational therapeutic strategies.     

Palbociclib synergizes with BRAF and MEK inhibitors in treatment naïve melanoma but not after the development of BRAF inhibitor resistance

Increased CDK4 activity occurs in the majority of melanomas and CDK4/6 inhibitors in combination with BRAF and MEK inhibitors are currently in clinical trials for the treatment of melanoma. We hypothesize that the timing of the addition of CDK4/6 inhibitors to the current BRAF and MEK inhibitor regime will impact on the efficacy of this triplet drug combination. The efficacy of BRAF, MEK and CDK4/6 inhibitors as single agents and in combination was assessed in human BRAF mutant cell lines that were treatment naïve, BRAF inhibitor tolerant or had acquired resistance to BRAF inhibitors. Xenograft studies were then performed to test the in vivo efficacy of the BRAF and CDK4/6 inhibitor combination. Melanoma cells that had developed early reversible tolerance or acquired resistance to BRAF inhibition remained sensitive to palbociclib. In drug‐tolerant cells, the efficacy of the combination of palbociclib with BRAF and/or MEK inhibitors was equivalent to single agent palbociclib. Similarly, acquired BRAF inhibitor resistance cells lost efficacy to the palbociclib and BRAF combination. In contrast, upfront treatment of melanoma cells with palbociclib in combination with BRAF and/or MEK inhibitors induced either cell death or senescence and was superior to a BRAF plus MEK inhibitor combination. In vivo palbociclib plus BRAF inhibitor induced rapid and sustained tumor regression without the development of therapy resistance. In summary, upfront dual targeting of CDK4/6 and mutant BRAF signaling enables tumor cells to evade resistance to monotherapy and is required for robust and sustained tumor regression. Melanoma patients whose tumors have acquired resistance to BRAF inhibition are less likely to have favorable responses to subsequent treatment with the triplet combination of BRAF, MEK and CDK4/6 inhibitors.     

Real-World Experience with CDK4/6 Inhibitors for Metastatic HR+/HER2− Breast Cancer at a Single Cancer Center

BackgroundA study was initiated at Roswell Park Comprehensive Cancer Center to capture the real-world experience related to the use of CDK4/6 inhibitors (Ciclibs) for the treatment of metastatic hormone receptor-positive and HER2-negative breast cancer (HR+/HER2-).Patients and MethodsA total of 222 patients were evaluated who received CDK4/6 inhibitors in the period from 2015 to 2021. Detailed clinical and demographic information was obtained on each patient and used to define clinical and demographic features associated with progression-free survival on CDK4/6 inhibitor-based therapies.ResultsIn this real-world analysis, the majority of patients received palbociclib as the CDK4/6 inhibitor with letrozole or fulvestrant as the predominant endocrine therapies. The median progression-free survival (PFS) in the letrozole (27.6 months) and fulvestrant (17.2 months) groups were comparable to that observed in clinical trials. As expected, age at start of the treatment and menopausal status influenced endocrine therapy utilization but were not associated with PFS. Patients with recurrent disease had shorter PFS (P = .0024) than those presenting with de novo metastasis. The presence of visceral metastasis trended toward shorter PFS (P = .051). Similarly, prior endocrine therapy (P = .003) or chemotherapy (P = .036) was associated with shorter PFS. Body mass index was not associated with PFS or with dose interruption and/or modification. While the number of minorities in this analysis is limited (n = 26), these patients as a group had statistically shorter PFS on treatment (P = .002).ConclusionsThe real-world progression-free survival with CDK4/6 inhibitors mimics that observed in the clinical trial. A number of clinical and demographic features were associated with PFS on CDK4/6 inhibitor-based therapy. Further studies are ongoing to validate these findings incorporating additional cancer centers.

This article reports a real-world experience related to the use of CDK4/6 inhibitors for the treatment of metastatic hormone receptor-positive and HER2-negative breast cancer, focusing on clinical and demographic features associated with progression-free survival.

Implications for PracticeThis study provides the real-world experience with the use of CDK4/6 inhibitors in the treatment of metastatic HR+/HER2− breast cancer. The work defines clinical and demographic features that impact the response to these agents and could offer guidance in preferred strategies for select manifestations of the disease. The study also suggests the need for more study of under-represented minority populations.     

Aspects biologiques,précliniques et cliniques de l’association de radiothérapie et d’inhibiteur de CDK 4/6

Several clinical studies have shown that CDK4/6 inhibitors (CDK4/6i) improve survival in patients with metastatic or locally advanced HR-positive, HER-2-negative breast cancer (BC). The aim of this review was to synthesize the biological, preclinical and clinical aspects of the treatment of BC with CDK4/6i, with a focus on the combination of CDK4/6i and radiotherapy. The DNA damage induced after exposure of cells to ionizing radiation activates control pathways that inhibit cell progression in the G1 and G2 phases and induce a transient delay in progression in the S phase. These checkpoints are in particular mediated by cyclin-dependent kinases (CDK) 4/6 activated by cyclin D1. Several preclinical studies have shown that CDK4/6i could be used as radiosensitizers in non-small cell lung cancer, medulloblastoma, brainstem glioma and breast cancer. CDK4/6 inhibition also protected against radiation-induced intestinal toxicities by inducing redistribution of quiescent intestinal progenitor cells, making them less radiosensitive. Clinical data on the combination of CDK inhibitors and radiotherapy for both locoregional and metastatic irradiation are based on retrospective data. Nevertheless, the most optimal therapeutic sequence would be radiotherapy followed by palbociclib. Pending prospective clinical trials, the concomitant combination of the two treatments should be done under close supervision.     

Ribociclib Plus Letrozole in Patients with Hormone Receptor-positive,HER2-negative Advanced Breast Cancer with No Prior Endocrine Therapy: Subgroup Safety Analysis from The Phase 3b CompLEEment-1 Trial

BackgroundThe CDK4/6 inhibitor, ribociclib in combination with endocrine therapy significantly improved progression-free survival in the first line setting in post-menopausal patients with HR+/HER2− advanced breast cancer (ABC) in a pivotal phase 3, placebo-controlled trial (MONALEESA-2) and demonstrated superior overall survival in premenopausal patients with HR+/HER2− ABC (MONALEESA-7). The multinational, phase 3b, CompLEEment-1 trial, which assessed the safety and efficacy of ribociclib plus letrozole in a broader population of patients who have not received prior endocrine therapy for advanced disease, is the largest phase 3 clinical trial to date to evaluate the safety and efficacy of a CDK4/6 inhibitor. We report a subanalysis of data from patients (N = 339) enrolled in the central and south European countries of the SERCE (Southern Europe, RUC, Central Europe) cluster of CompLEEment-1.Patients and methodsMen and women of any menopausal status with HR+/HER2− ABC received once-daily oral ribociclib 600 mg (3-weeks on/1-week-off), plus letrozole 2.5 mg continuously. Men/premenopausal women also received a GnRH-agonist. The primary outcome was the number of patients with adverse events (AEs) over a timeframe of approximately 36 months. Time-to-progression, overall response rate, and clinical benefit rate were also measured.ResultsSafety results in the SERCE subgroup were consistent with those in the pivotal clinical trials of ribociclib in combination with endocrine therapy. Treatment-related AEs leading to dose adjustments/interruption occurred in 63.1% of patients but led to treatment discontinuation in only 10.6%. The most common treatment-related AEs of grade ≥ 3 were neutropenia and transaminase elevations. There were no fatal treatment-related events.ConclusionsThese findings from the SERCE subgroup support the safety and manageable tolerability of ribociclib in a broad range of patients with HR+/HER2− ABC more representative of patients in real-world clinical practice.Key words: CDK4/6 inhibitor, ribociclib, HR+, HER2−, advanced breast cancer, CompLEEment-1 trial