Uses

Palbociclib is a CDK4/6 inhibitor indicated for adults with hormone receptor (HR)-positive, HER2-negative advanced or metastatic breast cancer, in combination with an aromatase inhibitor as initial endocrine-based therapy or with fulvestrant following disease progression on prior endocrine therapy. It is also indicated with inavolisib and fulvestrant for endocrine-resistant, PIK3CA-mutated HR+/HER2- locally advanced or metastatic breast cancer.

Do not use if

No formal contraindications listed in the FDA label. However, avoid use in pregnancy due to potential fetal harm. Concomitant use with strong CYP3A inhibitors should be avoided.

Side effects

Most common adverse reactions include neutropenia (the most frequent dose-limiting toxicity), leukopenia, infections, fatigue, nausea, alopecia, anemia, and diarrhea. Interstitial lung disease/pneumonitis has been reported and can be fatal.

Warnings

Monitor complete blood count before treatment, at the start of each cycle, and as clinically indicated due to risk of severe neutropenia. Monitor for signs of ILD/pneumonitis. Advise patients of reproductive age to use effective contraception during and after treatment.

How it works

Palbociclib inhibits cyclin-dependent kinases 4 and 6 (CDK4/6), which are downstream effectors of estrogen receptor signaling. Inhibition prevents phosphorylation of the retinoblastoma protein (Rb), blocking cell cycle progression from G1 to S phase and reducing tumor cell proliferation.

Storage

Store at 20–25°C; excursions permitted between 15–30°C. Keep in original container.