FDA Expands Label for Palbociclib (Ibrance) in Metastatic Breast Cancer

Palbociclib plus fulvestrant is superior to fulvestrant alone

The FDA has approved a new indication expanding the use of palbociclib (Ibrance, Pfizer) 125-mg capsules, a therapy for metastatic breast cancer. Palbociclib is now approved for the treatment of hormone receptor-positive (HR+), human epidermal growth factor receptor 2-negative (HER2–) advanced or metastatic breast cancer in combination with fulvestrant in women with disease progression after endocrine therapy.

The supplemental new drug application for palbociclib was reviewed and approved under the FDA’s breakthrough therapy designation and priority review programs, based on results from the phase 3 PALOMA-3 trial in pre-, peri-, and post-menopausal women with HR+, HER2– metastatic breast cancer whose disease had progressed on or after endocrine therapy in the adjuvant or metastatic setting.

Palbociclib, first approved in February 2015, is also indicated for the treatment of HR+, HER2– advanced or metastatic breast cancer in combination with letrozole as initial endocrine-based therapy in postmenopausal women. The indication in combination with letrozole was approved based on progression-free survival (PFS).

Palbociclib is the first and only cyclin-dependent kinase 4/6 (CDK 4/6) inhibitor approved by the FDA.

The PALOMA-3 trial enrolled 521 women, regardless of menopausal status. The subjects were randomly assigned to receive palbociclib plus the standard-of-care hormonal therapy fulvestrant (Faslodex, AstraZeneca) or placebo plus fulvestrant. This study demonstrated that palbociclib in combination with fulvestrant prolonged PFS compared with placebo plus fulvestrant in women with HR+, HER2– metastatic breast cancer whose disease had progressed on or after prior endocrine therapy. Women in the palbociclib/fulvestrant arm had a median PFS of 9.5 months, which represented a significant improvement compared with 4.6 months in the placebo/fulvestrant arm (hazard ratio, 0.461; P < 0.0001). The confirmed overall response rates in patients with measurable disease were 25% for palbociclib/fulvestrant compared with 11% for placebo/fulvestrant. The durations of response were 9.3 months in the palbociclib/fulvestrant arm and 7.6 months in the placebo/fulvestrant arm.

The warnings and precautions associated with palbociclib include neutropenia, pulmonary embolism, and embryo-fetal toxicity. The most common adverse events reported in the PALOMA-3 trial of palbociclib plus fulvestrant compared with placebo plus fulvestrant included neutropenia (83% vs. 4%, respectively), leukopenia (53% vs. 5%), infections (47% vs. 31%), fatigue (41% vs. 29%), nausea (34% vs. 28%), anemia (30% vs. 13%), stomatitis (28% vs. 13%), headache (26% vs. 20%), diarrhea (24% vs. 19%), thrombocytopenia (23% vs. 0%), constipation (20% vs. 16%), vomiting (19% vs. 15%), alopecia (18% vs. 6%), rash (17% vs. 6%), decreased appetite (16% vs. 8%), and pyrexia (13% vs. 5%).

Sources: Pfizer; February 19, 2016; and Ibrance Prescribing Information; February 2016.