Ribociclib Population Pharmacokinetics and Pharmacokinetic/Pharmacodynamic Analysis of Neutrophils in Cancer Patients

The population pharmacokinetics (popPK) of ribociclib and population pharmacokinetic/pharmacodynamic (PK/PD) relationship between ribociclib and absolute neutrophil count (ANC) were characterized in patients with cancer. PopPK and ANC PK/PD modeling were both conducted in 2 rounds per data availability. Initial models were developed based on data sets from early-phase trials and qualified using external data from the phase III MONALEESA-2 trial. The second round of analyses was performed using updated data sets that included 2 more phase III trials (MONALEESA-3 and -7). The popPK and ANC PK/PD models adequately described the data and demonstrated reasonable predictive ability. Covariate analysis showed that ribociclib PK were not affected by age, sex, race, baseline Eastern Cooperative Oncology Group (ECOG) status (grade 1), mild/moderate renal impairment, mild hepatic impairment, or concomitant use of combination partners, including aromatase inhibitors (letrozole, anastrozole) or fulvestrant, proton-pump inhibitors, or weak cytochrome P450 3A4/5 inhibitors. Body weight had no impact on ribociclib clearance to warrant dose adjustment. The ANC PK/PD relationship was not affected by age, weight, sex, race, baseline ECOG status (grade 1), or concomitant use of letrozole, anastrozole, or fulvestrant. The PK/PD analysis confirmed reversibility of ribociclib's effect on ANC; it also suggested that lowering the dose of ribociclib would mitigate ANC decrease and neutropenia risk. The popPK and ANC PK/PD analyses support the use of ribociclib in combination with an aromatase inhibitor or fulvestrant in patients with hormone receptor-positive, human epidermal growth factor receptor-2-negative advanced or metastatic breast cancer without dose adjustment in subpopulations, and the use of dose interruption/reduction to mitigate potential treatment-emergent neutropenia.

Abemaciclib, a third CDK 4/6 inhibitor for the treatment of hormone receptor-positive, human epidermal growth factor receptor 2-negative advanced or metastatic breast cancer

INTRODUCTION

The field of metastatic luminal breast cancer (hormone receptor positive, HER-2 negative) is dynamic and evolving, harboring some of the most significant therapeutic advances in medical oncology. Over the last decade, many pivotal trials showed excellent results with drastic improvements in survival as well as the quality of life of metastatic luminal breast cancer patients.

AREAS COVERED

The successful inhibition of the cyclinD/cyclin-dependent kinases 4 and 6 (CDK4/6)-retinoblastoma protein (RB) pathway with potent CDK4/6 inhibitors improved the outcome of advanced luminal breast cancers. Abemaciclib is the third CDK 4/6 inhibitor arriving to the market after palbociclib and ribociclib. Here, we describe the biology of the CDK4/6 pathway and summarize clinical data of previously published pivotal trials emphasizing the efficacy and toxicity of abemaciclib. The aim was to define its place in the current guidelines and to make a brief comparison with other available drugs of same class in the absence of cross trials comparison.

EXPERT OPINION

As there are no available biomarkers to predict response or resistance to abemaciclib, the promising overall survival data of MONARCH-2 could possibly impact the clinician's choice to optimize treatment for endocrine-resistant metastatic breast cancer.

Recent advances in understanding breast cancer and emerging therapies with a focus on luminal and triple-negative breast cancer

Breast cancer is a global health issue. For decades, breast cancer was classified into many histological subtypes on the basis of microscopic and immunohistochemical evaluation. The discovery of many key genomic driver events involved in breast cancer carcinogenesis resulted in a better understanding of the tumor biology, the disease heterogeneity and the prognosis leading to the discovery of new modalities of targeted therapies and opening horizons toward a more personalized medicine. In recent years, many therapeutic options emerged in the field of metastatic breast carcinoma, especially for the luminal subtypes. They were able to transform the course of the disease while maintaining quality of life. However, the options are still limited for triple-negative breast cancer, but the better knowledge of its complex biology and the discovery of molecular targets are promising for more efficient novel therapies.

Efficacy of Palbociclib Combinations in Hormone Receptor-Positive Metastatic Breast Cancer Patients After Prior Everolimus Treatment

PURPOSE

Outcome data on hormone receptor positive (HR+), human epidermal growth factor receptor 2 (HER2) nonamplified (HER2-) metastatic breast cancer (MBC) treated with palbociclib after treatment with everolimus are lacking. The PALOMA-3 trial, showing benefit of palbociclib plus fulvestrant compared to fulvestrant alone in HR+HER2- MBC after progression while receiving endocrine therapy excluded women previously treated with everolimus. The objective of this study was to examine outcomes of HR+HER2- MBC with prior exposure to everolimus while receiving palbociclib-based therapy.

PATIENTS AND METHODS

A retrospective, single-institute review was conducted of HR+HER2- MBC from January 2014 to November 2016 in patients treated with palbociclib after prior treatment with everolimus. Progression-free survival (PFS) was defined as the time from initiation of palbociclib to the date of progression as determined by the treating physician based on radiologic, biochemical, and/or clinical criteria. Response rates were determined on the basis of available radiologic data. Objective response rate (ORR) was defined as the rate of any complete or partial responses; clinical benefit rate (CBR) was the rate of complete response, partial response, or stable disease for at least 24 weeks.

RESULTS

Twenty-three patients with a mean (range) age of 68 (42-81) years were identified. Kaplan-Meier estimate showed median PFS of 2.9 months (95% confidence interval, 2.1-4.2); ORR was 0 of 23 and CBR was 4 (17.4%) of 23. In the PALOMA-3 trial, median PFS, ORR, and CBR of palbociclib cohort were 9.5 months (95% confidence interval, 9.2-11.0), 19%, and 67%, respectively.

CONCLUSION

There is a limited clinical activity of palbociclib combinations after progression with everolimus combination therapy. Further studies are necessary to confirm these findings.

SABCS 2017: lifestyle factors, hormone receptor-positive advanced disease, liquid biopsies, and prognosis

This article reviews the clinically most relevant presentations at the San Antonio Breast Cancer Symposium (SABCS) 2017 on the topics lifestyle factors, hormone receptor-positive advanced disease, liquid biopsies, and prognosis.

In a retrospective analysis of the Women’s Health Initiative Observational Study, a reduction in the body mass index (BMI) of at least 5% within 3 years significantly reduced the risk of breast cancer compared to women with a stable weight (HR 0.77; 95% CI 0.78–0.98). In the MONALEESA-7 trial investigating ribociclib or placebo in combination with endocrine therapy as first-line treatment in pre- and perimenopausal women with hormone receptor-positive, human epidermal growth factor 2 (HER2)-negative metastatic breast cancer, a significantly longer progression-free survival was shown for patients treated with ribociclib compared to the placebo group (23.8 vs. 13.0 months; HR 0.55; 95% CI 0.43–0.72; P < 0.001). In a pooled toxicity and efficacy analysis of elderly women treated with a cyclin-dependent kinase 4/6 (CDK4/6) inhibitor in combination with an aromatase inhibitor in first-line, toxicities of higher grade were more common in elderly compared to younger patients, despite comparable efficacy. And the Clinical Treatment Score post-5 years (CTS5), accurately estimated the risk of late recurrence after 5 years of adjuvant endocrine treatment using routinely available clinical parameters.

Cure in metastatic breast cancer

Oligometastatic disease characterizes a distinct subgroup of metastatic breast cancer patients that might benefit from different treatment strategies to achieve long-lasting remission and potentially cure. Those long-lasting remissions are reported after locoregional treatment of the primary tumor and all metastatic sites in several case series; however, unlike other tumor entities, prospective data are lacking. Furthermore, tumor eradication by excellent systemic anticancer therapy with novel chemotherapies and targeted agents can lead to long-term survival. In addition, reactivation of the host immune defense by immuno-oncologic drugs can achieve long-lasting tumor control. So far, unfortunately, checkpoint inhibitors as monotherapy have led to responses only in a small percentage of patients with metastatic breast cancer. This short review summarizes available data on long-lasting remissions and potential cure in metastatic breast cancers. It describes and discusses data on locoregional treatment, chemo-, antibody- and immunotherapy and tries to select individual patients for whom a multidisciplinary treatment approach with curative intention might be an option to achieve long-term survival.

Role of cyclin-dependent kinase 4/6 inhibitors in the current and future eras of cancer treatment

Cyclin-dependent kinase 4/6 inhibitors, which act by inhibiting progression from the G1 to S phases of the cell cycle, include palbociclib, ribociclib, abemaciclib, and trilaciclib. Palbociclib and ribociclib are currently food and drug administration-approved for use in combination with aromatase inhibitors in postmenopausal women with metastatic hormone receptor-positive, human epidermal growth factor receptor 2-negative breast cancer. Palbociclib is also food and drug administration-approved for use in combination with fulvestrant in hormone receptor-positive, human epidermal growth factor receptor 2-negative breast cancer progressing after endocrine therapy. Abemaciclib is the newest cyclin-dependent kinase 4/6 inhibitor to gain Food and Drug Administration (FDA) approval, specifically as monotherapy for hormone receptor-positive, human epidermal growth factor receptor 2-negative metastatic breast cancer previously treated with chemotherapy and endocrine therapy. Abemaciclib also shares a similar indication with palbociclib for use in combination with fulvestrant in hormone receptor-positive, human epidermal growth factor receptor 2-negative breast cancer progressing after endocrine therapy. Trilaciclib use remains largely investigational at this time. However, despite FDA-approval for only metastatic hormone receptor-positive, human epidermal growth factor receptor 2-negative breast cancer, all four cyclin-dependent kinase 4/6 inhibitors have shown promise in hematologic malignancies and non-breast solid tumors. Although further research is needed, cyclin-dependent kinase 4/6 inhibitors represent intriguing developments in the treatment of various malignancies, including those with such poor prognoses as glioblastoma multiforme, mantle cell lymphoma, and metastatic melanoma. We discuss the approved indications, current research, and areas of future exploration for palbociclib, ribociclib, abemaciclib, and trilaciclib.

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.

A Review of Fulvestrant in Breast Cancer

Fulvestrant is a selective estrogen receptor degrader that binds, blocks and degrades the estrogen receptor (ER), leading to complete inhibition of estrogen signaling through the ER. This review article further explains the mechanism of action of the drug and goes on to review the trials carried out to optimize its dosing. Multiple trials have been undertaken to compare fulvestrant with other endocrine treatments, and results have shown it to have similar efficacy to anastrozole, tamoxifen and exemestane at 250 mg every 28 days. However, when given at 500 mg every 28 days, with an extra loading dose on day 14, it has demonstrated an improved progression-free survival (PFS) compared to anastrozole. We look at how fulvestrant has been used in combination with CDK4/6 inhibitors such as palbociclib (PALOMA-3) and ribociclib (MONALEESA-3) and drugs targeting the PI3K/AKT/mTOR pathway such as pictilisib (FERGI) and buparlisib (BELLE-2 and BELLE-3). We then go on to describe a selection of the ongoing clinical trials looking at combination therapy involving fulvestrant. Finally, we review the effect of fulvestrant in patients who have developed resistance to aromatase inhibitors via ESR1 mutation, where it has been shown to offer a PFS benefit that is further improved by the addition of the CDK4/6 inhibitor palbociclib. Whilst fulvestrant is clearly an effective drug as monotherapy, we believe that its role in the treatment of ER-positive breast cancer may be best reserved for combination therapy, and whilst there are multiple trials currently in progress, it would appear that the combination with CDK4/6 inhibitors would offer the greatest promise in terms of balancing benefit with toxicity.