Abemaciclib Significantly Reduces Cell Proliferation Biomarker in Early-Stage Breast Cancer

Cyclin-dependent kinase inhibitor reduces Ki67 expression and shows promise in breast cancer treatment.

After 2 weeks of treatment, abemaciclib met its primary endpoint in a phase 2 trial by reducing Ki67 expression in women with early-stage breast cancer. Ki67 represents a key biomarker of cancer cell proliferation.

The findings were presented during the official press program at the 2016 San Antonio Breast Cancer Symposium, according to an Eli Lilly press release.

Abemaciclib is an oral cell cycle inhibitor, designed to block the growth of cancer cells by specifically inhibiting cyclin-dependent kinases (CDK), CDK4, and CDK6.

In the randomized, open-label, multi-center, phase 2 neoMONARCH study, investigators evaluated 225 postmenopausal women with previously untreated early-stage hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2-) breast cancer. The participants had at least 1 measurable tumor ≥1 cm, adequate organ function, and an ECOG performance status of ≤1.

Patients were randomized to receive either 150 mg abemaciclib monotherapy twice-daily for 2 weeks; 150 mg abemaciclib twice-daily plus once-daily 1 mg anastrozole for 2 weeks; or 1 mg anastrozole monotherapy once-daily for 2 weeks.

The primary objective of the study was to assess the percentage change of Ki67 in the breast tumor after 2 weeks of therapy from baseline. The results of the study showed that abemaciclib monotherapy, and abemaciclib in combination with anastrozole, significantly reduced Ki67 more than anastrozole monotherapy in neoadjuvant HR+/HER2 breast cancer.

Following the initial 2 weeks of randomized treatment, all participants went on to receive twice-daily 150 mg abemaciclib plus 1 mg anastrozole for an additional 14 to 22 weeks.

The study also included the prophylactic use of 2 mg loperamide twice-daily in combination with abemaciclib for the first 28 days. There were no new safety signals observed for abemaciclib when administered in combination with anastrozole, according to the press release.

“Lilly is committed to the scientific discovery and development of new therapies that change current standards of cancer care,” said Sue Mahony, PhD, senior vice president and president, Lilly Oncology. “The neoMONARCH data are encouraging and continue to inform our understanding of how abemaciclib should be used as both a single-agent therapy or in combination with aromatase inhibitors, such as anastrozole, in the early-stage setting.”