Palbociclib plus letrozole in estrogen receptor-positive advanced/recurrent endometrial cancer: Double-blind...

The CDK4/6 inhibitor palbociclib inhibits cyclin A, which is overexpressed in endometrial cancer. Combining palbociclib with endocrine therapy improves efficacy in hormone receptor-positive breast cancer. We investigated palbociclib combined with endocrine therapy for estrogen receptor-positive advanced/recurrent endometrial cancer.

This placebo-controlled double-blind, randomized phase II screening trial (NCT02730429) enrolled women with measurable/evaluable estrogen receptor-positive endometrioid endometrial cancer that was primary metastatic or had relapsed after ≥1 prior systemic therapy. Patients were randomized in a 1:1 ratio, stratified by number of prior chemotherapy lines, measurable versus evaluable non-measurable disease, and prior medroxyprogesterone/megestrol acetate treatment, to receive oral letrozole 2.5 mg on days 1-28 plus either oral palbociclib 125 mg or placebo on days 1-21, repeated every 28 days until disease progression or unacceptable toxicity. The primary end point was investigator-assessed progression-free survival (PFS).

Among 77 patients randomized between February 16, 2017, and December 21, 2018, 73 were treated (36 with palbociclib-letrozole, 37 with placebo-letrozole). Median follow-up was 21.9 (95 % CI, 16.7 to 22.3) months. Median PFS was 8.3 (95 % CI, 4.6 to 11.2) versus 3.1 (95 % CI, 2.7 to 6.8) months, respectively. In a landmark analysis at 12 months the PFS hazard ratio was 0.57 (95 % CI, 0.32 to 0.99; P = .044). Grade ≥ 3 adverse events were more common with palbociclib-letrozole (67 %) than placebo-letrozole (30 %), most commonly neutropenia (44 % v 0 %, respectively).

These results support a potential role of the palbociclib-letrozole combination as treatment for hormone receptor-positive advanced/recurrent endometrial cancer. Based on these encouraging results, phase III evaluation of letrozole combined with a CDK4/6 inhibitor is planned.

NCT02730429.