An ongoing study will allow researchers to determine the comparability of abemaciclib plus fulvestrant in progression-free survival (PFS) and objective response rate (ORR) compared with standard-of-care chemotherapy.

The study was presented at the 2019 San Antonio Breast Cancer Symposium in San Antonio, TX.

Abemaciclib is a potent oral cyclin-dependent kinase (CDK) 4/6 inhibitor that has previously demonstrated statistically significant improvement in PFS and ORR in combination with endocrine therapy (ET) in patinets with hormone receptor positive (HR+) or human epidermal growth factor receptor 2-negative (HER2-) advanced and metastatic breast cancer in phrase 3 studies.

Cytotoxic chemotherapy is often initiated early in the course of HR+, HER2- advanced breast cancer despite absence of visceral crises, potentially denying patients effective and tolerable standard-of-care regimens containing ET.

The current study, known as 13Y-MC-JPCU, is a multicenter, open-label, randomized study and includes abemaciclib in combination with fulvestrant compared to chemotherapy in women with HR+, HER2- locally advanced or metastatic breast cancer who have a poor prognosis due to visceral metastases. Researchers will examine ORR in addition to PFS, time to response, and duration of response.

Approximately 300 patients will be randomized to either a combination of abemaciclib and fulvestrant or a physician's choice of chemotherapy such as capecitabine, docetaxel, nabpaclitaxel, or paclitaxel. The study will include women who are postmenopausal HR+, HER2- patients with locally advanced recurrent and unresectable or metastatic HR+, HER2- breast cancer and 1 site of visceral metastasis as well as disease progression after 1 line of ET in neoadjuvant or metastatic setting.

The study is designed to demonstrate comparability using a 10% ORR margin and a 20% PFS margin. Researchers will declare the treatment options comparable if the posterior probability, or the probability that the event will occur, true difference is less than the comparability margin at least 80%.

A randomized trial of abemaciclib in combination with fulvestrant compared to chemotherapy in women with HR+, HER2- advanced breast cancer with visceral metastases. Presented at the San Antonio Breast Cancer Symposium.