FDA Expands Palbociclib Approval for Breast Cancer

“The Food and Drug Administration (FDA) has granted an expanded indication for the cyclin-dependent kinase 4/6 inhibitor palbociclib (Ibrance). The drug is now approved for use in combination with fulvestrant in women with hormone receptor (HR)-positive, HER2-negative advanced or metastatic breast cancer whose disease progressed following endocrine therapy.

“Palbociclib was initially approved in February 2015 for the treatment of estrogen receptor–positive, HER2-negative metastatic breast cancer, in women who had not yet received endocrine therapy. The new approval was granted under the FDA’s breakthrough therapy designation.

“The additional indication for palbociclib is based on results from the PALOMA-3 trial, which was stopped early in April 2015 after an interim analysis showed benefit in combination with fulvestrant when compared to fulvestrant and placebo.”


Ibrance Trial Stopped Early Because of Strong Evidence of Drug's Efficacy in Metastatic ER+ HER2- Breast Cancer

“Pfizer Inc. PFE, +1.01% today announced that the Phase 3 PALOMA-3 trial for IBRANCE® (palbociclib) met its primary endpoint of demonstrating an improvement in progression-free survival (PFS) for the combination of IBRANCE plus fulvestrant compared with fulvestrant plus placebo in women with hormone receptor positive (HR+), human epidermal growth factor receptor 2 negative (HER2-) metastatic breast cancer following disease progression during or after endocrine therapy. The study was stopped early due to efficacy based on an assessment by an independent Data Monitoring Committee (DMC). These are the first randomized Phase 3 trial results for IBRANCE, a new anti-cancer medicine with the novel mechanism of cyclin-dependent kinase 4/6 (CDK 4/6) inhibition.

“ ‘The results of this trial are especially important because they help us understand the potential of IBRANCE to improve outcomes in patients with this difficult to treat cancer. We’re gratified to be able to stop the trial early and are engaging in discussions with health authorities regarding a regulatory path forward,’ said Dr. Mace Rothenberg, senior vice president of Clinical Development and Medical Affairs and chief medical officer for Pfizer Oncology.

“The adverse events observed with IBRANCE in combination with fulvestrant in PALOMA-3 were generally consistent with their respective known adverse event profiles. Detailed efficacy and safety results from PALOMA-3 will be submitted for presentation at the American Society of Clinical Oncology (ASCO) 2015 Annual Meeting.”


An F876L Mutation in Androgen Receptor Confers Genetic and Phenotypic Resistance to MDV3100 (Enzalutamide)

“Castration resistant prostate cancer (CRPC) is the most aggressive, incurable form of prostate cancer. MDV3100 (enzalutamide), an antagonist of the androgen receptor (AR), was approved for clinical use in men with metastatic CRPC. Although this compound showed clinical efficacy, many initial responders later developed resistance. To uncover relevant resistant mechanisms, we developed a model of spontaneous resistance to MDV3100 in LNCaP prostate cancer cells. Detailed characterization revealed that emergence of F876L mutation in AR correlated with blunted AR response to MDV3100 and sustained proliferation during treatment. Functional studies confirmed that AR-F876L confers an antagonist-to-agonist switch that drives phenotypic resistance. Lastly, treatment with distinct anti-androgens or CDK4/6 inhibitors effectively antagonized AR-F876L function. Together, these findings suggest that emergence of F876L may 1) serve as a novel biomarker for prediction of drug sensitivity, 2) predict a “withdrawal” response to MDV3100, and 3) be suitably targeted with other anti-androgens or CDK4/6 inhibitors.”