CDK4/6 Inhibition - Therapy Sequences and the Quest to Find the Best Biomarkers - an Overview of Current Programs

In recent years, new targeted therapies have been developed to treat patients with hormone receptor-positive (HR+)/human epidermal growth factor receptor 2-negative (HER2-) breast cancer. Some of these therapies have not just become the new therapy standard but also led to significantly longer overall survival rates. The cyclin-dependent kinase 4 and 6 inhibitors (CDK4/6i) have become the therapeutic standard for first-line therapy. Around 70 - 80% of patients are treated with a CDK4/6i. In recent years, a number of biomarkers associated with progression, clonal selection or evolution have been reported for CDK4/6i and their endocrine combination partners. Understanding the mechanisms behind treatment efficacy and resistance is important. A better understanding could contribute to planning the most effective therapeutic sequences and utilizing basic molecular information to overcome endocrine resistance. One study with large numbers of patients which aims to elucidate these mechanisms is the Comprehensive Analysis of sPatial, TempORal and molecular patterns of ribociclib efficacy and resistance in advanced Breast Cancer patients (CAPTOR BC) trial. This overview summarizes the latest clinical research on resistance to endocrine therapies, focusing on CDK4/6 inhibitors and discussing current study concepts.

Antitumor response and quality of life: is there a need to sacrifice? Clinical observation: long-term and safe control of the disease using a combination of ribociclib with letrozole. Case report

Metastatic luminal B HER2-negative breast cancer (HR+/HER2- mBC) occupies a leading place in the global structure of morbidity and mortality among women. The current gold standard of first-line treatment is the combination of CDK4/6 inhibitors with aromatase inhibitors, among which ribociclib with letrozole is distinguished. According to the MONALEESA-2 study, the addition of ribociclib to letrozole significantly increased the median overall survival to 63.9 months, reducing the risk of death by 24%. The safety profile of the combination is manageable, and the development of adverse events led to the interruption of therapy only in 7.5% of cases. A study of the actual clinical practice of CompLEEment-1 also confirmed the safety and effectiveness of the combination. Maintaining and improving the quality of life is one of the main tasks in the treatment of patients with HR+/HER2- mBC. According to the MONALEESA-2 study, the addition of ribociclib significantly affects the maintenance of quality of life and leads to a decrease in the intensity of pain syndrome. The published data allowed us to assign a combination of ribociclib and letrozole 4 points on the ESMO-MCBS scale. The safety of long-term use of the combination in the first line of treatment illustrated by clinical observation. The patient's progression-free survival during therapy was 40 months, which significantly exceeds the data of the MONALEESA-2 and CompLEEment-1 studies. The maximum effect (partial response according to RECIST 1.1 -40%) achieved after 24 weeks and persisted for 24 months. Clinically, the patient noted a decrease in the severity of the pain syndrome after 8 weeks of therapy. Against the background of therapy, it was possible to maintain the quality of life without sacrificing antitumor efficacy.

Vitiligo-Like Lesions in a Patient with Metastatic Breast Cancer Treated with Cyclin-Dependent Kinase (CDK) 4/6 Inhibitor: A Case Report and Literature Review

Background

Cyclin-dependent kinase (CDK) 4/6 inhibitors have revolutionized the treatment landscape of hormone receptor-positive (HR⁺), human epidermal growth factor receptor 2-negative (HER2⁻) metastatic breast cancer, with an impressive efficacy and safety profile. Cytopenia is the main adverse event, which is both predictable and manageable. Here, we report a case of CDK4/6 inhibitor-induced vitiligo-like lesions. Vitiligo or vitiligo-like lesions are a rare adverse event; only a few cases are reported in the literature.

Case Presentation

A 71-year-old female patient was diagnosed initially with early-stage right breast cancer (HR⁺/HER2⁻) and was treated with breast-conserving surgery followed by chemotherapy, radiotherapy, and hormonal therapy. A few years later, she developed metastatic disease to the hilar lymph nodes, and to multiple skeletal sites, including the left scapula, left shoulder, left iliac bone, and dorsal vertebrae, for which she was treated with ribociclib and letrozole. While on treatment, she developed hypopigmented lesions involving both hands, feet, and face, which were described as vitiligo-like lesions.

Conclusion

CDK4/6 inhibitor-induced vitiligo is a rare and unpredictable adverse event. This case report highlights the rarity of this adverse event, the dilemma related to the optimal treatment, and decisions related to continuation, holding, or switching CDK4/6 inhibitors.

Patient-Reported Outcomes in Patients With PIK3CA-Mutated Hormone Receptor-Positive, Human Epidermal Growth Factor Receptor 2-Negative Advanced Breast Cancer From SOLAR-1

PURPOSE

In the phase III SOLAR-1 trial (NCT02437318), the PI3Kα-selective inhibitor and degrader alpelisib significantly improved median progression-free survival when added to fulvestrant in patients with phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit alpha (PIK3CA)-mutated, hormone receptor-positive, human epidermal growth factor receptor 2-negative advanced breast cancer. We assessed health-related quality of life using patient-reported outcome measures in these patients.

MATERIALS AND METHODS

In the PIK3CA-mutant cohort, 341 patients were randomly assigned 1:1 to receive alpelisib 300 mg daily or placebo plus fulvestrant 500 mg on days 1 and 15 of cycle 1 and on day 1 of subsequent 28-day cycles. Patient-reported outcomes were evaluated with the European Organisation for Research and Treatment of Cancer QoL of Cancer Patients and Brief Pain Inventory-Short Form questionnaires. Changes from baseline and time to 10% deterioration were analyzed using repeated measurement models and Cox models, respectively.

RESULTS

Global Health Status/QoL and functional status were maintained from baseline (mean changes < 10 points) in the alpelisib (overall change from baseline [95% CI], -3.50 [-8.02 to 1.02]) and placebo arms (overall change from baseline [95% CI], 0.27 [-4.48 to 5.02]). Overall treatment effect in Global Health Status/QoL was not significantly different between arms (-3.77; 95% CI, -8.35 to 0.80; P = .101). Time to 10% deterioration for Global Health Status/QoL was similar between arms (hazard ratio, 1.03; 95% CI, 0.72 to 1.48). Compared with placebo, deterioration in social functioning and in diarrhea, appetite loss, nausea or vomiting, and fatigue symptom subscales occurred with alpelisib. Numerical improvement in Worst Pain was observed with alpelisib versus placebo (42% v 32%, week 24; P = .090).

CONCLUSION

In SOLAR-1, there was no statistical difference in deterioration of Global Health Status/QoL between arms, whereas symptom subscales favored placebo for diarrhea, appetite loss, nausea or vomiting, and fatigue, known side effects of alpelisib. Treatment decisions must consider efficacy and tolerability; taken with clinical efficacy, these results support the benefit-risk profile of alpelisib in patients with hormone receptor-positive, human epidermal growth factor receptor 2-negative PIK3CA-mutated advanced breast cancer.

CDK4/6 inhibitor plus endocrine therapy for hormone receptor-positive, HER2-negative metastatic breast cancer: The new standard of care

Patients presenting with hormone receptor-positive (HR⁺ ), human epidermal growth factor receptor 2-negative (HER2^- ) metastatic breast cancer (MBC) are usually treated with endocrine therapy (ET), except if there is a concern about endocrine resistance or a need to achieve rapid disease control due to visceral crisis. The combination of CDK4/6 inhibitor + ET has now replaced single-agent ET as the standard first-line treatment; and it can also be considered a standard option in the second-line setting. This review briefly summarizes recently reported efficacy findings from the key phase III clinical trials of CDK4/6 inhibitor + ET in patients with HR⁺ /HER2^- MBC, including evidence that adding a CDK4/6 inhibitor to ET improves overall survival and does so without reducing patients' quality of life. There is still much to learn regarding the use of CDK4/6 inhibitors and how they may be optimally integrated into clinical practice. In particular, there is a need for specific biomarkers that help predict the likelihood of response or resistance to CDK4/6 inhibitor therapy; and for data to guide treatment decisions when a patient's disease progresses on a CDK4/6 inhibitor.

CDK4/6 Inhibitors in Hormone Receptor-Positive Metastatic Breast Cancer: Current Practice and Knowledge

Treatment paradigms in advanced hormone receptor (HR)-positive breast cancer were substantially transformed with cyclin-dependent kinase 4 and 6 inhibitors (CDK4/6i) approval. The addition of these drugs to endocrine treatment profoundly improved progression-free and overall survival. Additionally, other important endpoints, such as the response rate, time to chemotherapy, and a delay in quality of life deterioration, were positively impacted by CDK4/6 inhibitors' addition to the treatment of advanced HR-positive breast cancer. This review article will summarize current knowledge on CDK4/6 inhibitors in clinical practice for advanced HR-positive metastatic breast cancer, as well as describe recent efforts to more precisely characterize mechanisms of sensitivity and resistance to these drugs, both on the molecular and clinical characterization level.

Abemaciclib, a CDK4 and CDK6 inhibitor for the treatment of metastatic breast cancer

The addition of CDK4 and 6 inhibitors (abemaciclib, palbociclib or ribociclib) to endocrine therapy, as first-line treatment or following progression after initial endocrine therapy, significantly increased progression-free survival, objective response rates and in some trials overall survival, compared with endocrine therapy alone in HR+ and HER2- breast metastatic breast cancer. These CDK4 and 6 inhibitors are now approved in this context and have become a new standard of care. A hypothesis-generating exploratory analysis suggested that the addition of abemaciclib to endocrine therapy showed the largest effects in subgroups of women with indicators of poor prognosis, although these data require confirmation. This review provides updated clinical trial data for all three drugs in metastatic breast cancer, focusing on abemaciclib, the most recently approved agent.

Health-related quality of life in premenopausal women with hormone-receptor-positive, HER2-negative advanced breast cancer treated with ribociclib plus endocrine therapy: results from a phase III randomized clinical trial (MONALEESA-7)

Background:

This analysis evaluated patient-reported outcomes (PROs) to assess health-related quality of life (HRQoL) in the phase III MONALEESA-7 trial, which previously demonstrated improvements in progression-free survival (PFS) and overall survival (OS) with ribociclib (cyclin-dependent kinase 4/6 inhibitor) + endocrine therapy (ET) compared with placebo + ET in pre- and perimenopausal patients with hormone-receptor-positive, HER2-negative (HR+/HER2−) advanced breast cancer (ABC).

Methods:

The European Organisation for Research and Treatment of Cancer (EORTC) Quality of Life questionnaire C30 (QLQ-C30) and the EQ-5D-5L were used to evaluate HRQoL.

Results:

EORTC QLQ-C30 assessments were evaluable for 335 patients in the ribociclib arm and 337 patients in the placebo arm. Adherence rates at baseline and ⩾1 postbaseline time point were 90% and 83%, respectively. Patients treated with ribociclib + ET had a longer time to deterioration (TTD) ⩾ 10% in global HRQoL {hazard ratio (HR), 0.67 [95% confidence interval (CI), 0.52–0.86]}. TTD ⩾ 10% in global HRQoL was delayed in ribociclib-treated patients without versus with disease progression [HR, 0.31 (95% CI, 0.21–0.48)]. TTD ⩾ 10% in pain was longer with ribociclib + ET than with placebo + ET [HR, 0.65 (95% CI, 0.45–0.92)]. Patients who received a nonsteroidal aromatase inhibitor experienced similar benefits with ribociclib versus placebo in global HRQoL and pain.

Conclusion:

HRQoL was maintained longer in patients who received ribociclib + ET versus placebo + ET. These data, combined with previously reported improvements in PFS and OS, support a strong clinical benefit-to-risk ratio with ribociclib-based treatment in pre- and perimenopausal patients with HR+/HER2− ABC.

Are all cyclin-dependent kinases 4/6 inhibitors created equal?

The harnessing in clinical practice of cyclin-dependent kinases 4/6 inhibitors, namely palbociclib, ribociclib, and abemaciclib, has substantially changed the therapeutic approach for hormone receptor-positive metastatic breast cancer (BC). Phase II-III clinical trials evaluating the addition of these agents to standard endocrine therapy reported consistent improvements in response rates and progression-free survival as well as manageable toxicity profiles and excellent impact on patients' quality of life. Hence, pivotal trials provided comparable results among different cyclin-dependent kinases 4/6 inhibitors, there is an increasing interest in finding substantial differences in order to implement their use in clinical practice. The aim of this paper is to summarize the current evidences raised from preclinical and clinical studies on cyclin-dependent kinases 4/6 inhibitors in BC, focusing on differences in terms of pharmacological properties, toxicity profile, and patients' quality of life.

Why upfront use of CDK inhibitors for the treatment of advanced breast cancer may be wasteful, and how we can increase their value

Three Cyclin Dependent Kinase 4/6 (CDK) inhibitors have been approved by the United Stated Food and Drug Administration for front line treatment of advanced hormone receptor positive breast cancer based on improvements in progression free survival against endocrine monotherapy. Two clinical trials have so far reported results on overall survival but both are negative. CDK inhibitors are usually tolerated well but they do add to inconvenience and cost - for example, grade III-IV neutropenia occur at a frequency of over 60% requiring frequent blood work at least during the initial months of treatment. These drugs cost over $ 13,500 for a 4-week cycle in the United States, and are responsible for billions of dollars annually in drug cost alone. Importantly, many women with metastatic breast cancer do well for a long time with endocrine therapy alone and CDK inhibitors do not have a predictive marker. Selective use of these agents in later lines may improve substantially the convenience and cost without compromise in overall outcome. However, with results demonstrating impressive improvements in PFS published in major medical journals coupled with patients' natural desire for "best available" options, the trend among oncologists is to prescribe these drugs as the default front-line treatment. In this commentary I caution readers against over interpretation of results from the CDK inhibitor trials, describe adverse consequences of routine front-line use, and explain why selective use in later line may yield a higher value.