CDK4/6 inhibitors in advanced breast cancer, what is beyond?

Resistant to hormonal treatment considered the main clinical challenge in the management of advanced breast cancer (ABC). The use of CDK4/6 inhibitors (CDK4/6I) may change the treatment landscape. In this mandated review, we will focus on the applicable role of CDK4/6I in the management of HR+/HER2- ABC, mechanisms of resistance, and promising future implementation.

Targeting CDK4/6 pathways and beyond in breast cancer

Metastatic or advanced breast cancer (mBC/ABC) remains incurable despite many different systemic treatment options. Hormone receptor positive (HR+) disease represents the most common subtype in both early and advanced disease. A better understanding of the biology of this BC subtype, in particular regarding potential mechanisms of endocrine resistance, has led to the development of CDK4/6 inhibitors. All three selective CDK4/6 inhibitors, palbociclib, ribociclib and abemaciclib have shown to significantly improve progression-free survival (PFS) when combined to endocrine therapy as first-line treatment for patients with HR+/HER-2 negative ABC, who have progressed on or after adjuvant endocrine therapy. All three of them have also shown an improved PFS as 2nd line therapy for HR+/Her2 negative ABC. Their toxicity profile is favorable, with hematological toxicity (mainly neutropenia) being predominant, followed by diarrhea and fatigue. Quality of life has been maintained in the 1st line setting or improved in the 2nd line setting. Overall survival (OS) has been reported so far only in 2 out of 7 trials as first line therapy and the difference did not reach statistical significance. In this article we review the biology of CDK signaling pathway and its inhibitors, preclinical and clinical data of all three investigated selective CDK4/6 inhibitors and their toxicity. We also discuss how these agents are being included in current international guidelines and future directions for these agents in other subtypes of breast cancer, in both advanced disease and early-stage disease.

ESMO 2017-my personal highlights

This article is not intended to be a comprehensive review of all highlights presented at the recent ESMO Annual Meeting, but rather a summary from a personal point of view in three very different fields of oncology. Breast cancer and lung cancer are traditionally in the focus of interest, and again, relevant new data were presented. The third part of this overview is focused on novel treatment strategies in malignant lymphoma, a field that is also quickly evolving and traditionally underrepresented at meetings dealing with solid cancers.

Efficacy and safety of palbociclib in heavily pretreated patients with HR+/HER2- metastatic breast cancer

AIM

CDK4/6 inhibitors in the first and second treatment line in patients with HR+/HER2- metastatic breast cancer (mBC) in combination with hormonal therapy improve progression-free survival. Role of CDK4/6 inhibitors in further treatment lines remains unclear.

METHODS

Retrospective analysis of 24 HR+/HER2- heavily pretreated mBC patients is presented.

RESULTS

A total of 58.3% patients achieved stable disease. No objective response was observed. Median progression-free survival was 4.8 months; median overall survival was 11 months. Treatment was well tolerated.

CONCLUSION

Favorable toxicity profile and efficacy of palbociclib/aromatase inhibitors combination in heavily pretreated luminal mBC patients in this study emphasize the need for further investigation of such drugs in this population.

The next era of treatment for hormone receptor-positive, HER2-negative advanced breast cancer: Triplet combination-based endocrine therapies

Until recently, the standard of care for hormone receptor-positive (HR+) breast cancer was single-agent endocrine therapy, which aims to prevent estrogen receptor signaling. This therapeutic strategy has extended survival without the toxicity associated with chemotherapy, but primary endocrine therapy resistance is common, and secondary resistance develops over time. Adjunct downstream inhibition of the cyclin-dependent kinase (CDK)4/6 pathway, intended to delay and prevent endocrine therapy resistance, has further extended progression-free survival in patients receiving endocrine therapy; however, resistance still eventually develops in these patients. Addition of phosphatidylinositol-3 kinase (PI3K) or mammalian target of rapamycin (mTOR) inhibitors to combined CDK4/6 and endocrine inhibitor regimens may help prolong CDK4/6 inhibitor sensitivity. Early trials combining CDK4/6 inhibitors, PI3K or mTOR inhibitors, and endocrine therapy have shown encouraging signs of clinical activity. However, further research is needed to help understand the extent of treatment benefit from triplet therapy and where this strategy will fit in the treatment sequence for patients with HR+ breast cancer.

Strategies and Progress of Endocrine Therapy for Patients with Metastatic Breast Cancer

Breast cancer is one of the most prevalent cancers and the leading causes of cancer mortality in women worldwide and in China. For hormone receptor-positive (HR+) breast cancer, accounting for approximately 60-80% of breast cancer, endocrine therapy (ET) is the primary treatment strategy. For patients with HR+ metastatic breast cancer (MBC), there are many endocrine-based treatment options that can improve long-term outcomes and optimize quality of life. With the emergence and availability of new and effective agents, the options for ET have expanded in the last two decades. Although hormone therapy has been a standard of care for many decades, treatment must be individualized based on tumor biology and extent of disease. For example, the patients with impending organ failure may be treated with induction chemotherapy to improve organ function, followed by ET. For the patients who develop metastatic disease while on adjuvant ET, particularly when associated with organ failure, or for those with low expression of hormone receptors or expression of HER2, chemotherapy again may be a preferred initial treatment. ET blocks estrogen-driven tumor growth through different mechanisms; however, HR+ MBC can be intrinsically resistant or may acquire resistance to the treatment. Several targeted agents have been approved to use in combination with ET to improve response and delay development of resistance.