Palbociclib

What it is and how it works

Mechanism of Action Palbociclib is an inhibitor of cyclin-dependent kinases (CDK) 4 and 6. Cyclin D1 and CDK4/6 are downstream of signaling pathways which lead to cellular proliferation. In vitro, palbociclib reduced cellular proliferation of estrogen receptor (ER)-positive breast cancer cell lines by blocking progression of the cell from G1 into S phase of the cell cycle. Treatment of breast cancer cell lines with the combination of palbociclib and antiestrogens leads to decreased retinoblastoma (Rb) protein phosphorylation resulting in reduced E2F expression and signaling, and increased growth arrest compared to treatment with each drug alone.

Mechanism class: Kinase Inhibitors · Cytochrome P450 3A Inhibitors

Indications

is a kinase inhibitor indicated: • for the treatment of adult patients with hormone receptor (HR)-positive, human epidermal growth factor receptor 2 (HER2)-negative advanced or metastatic breast cancer in combination with: o an aromatase inhibitor as initial endocrine-based therapy ; or o fulvestrant in patients with disease progression following endocrine therapy. • in combination with inavolisib and fulvestrant for the treatment of adult patients with endocrine-resistant, PIK3CA -mutated, HR-positive, HER2-negative, locally advanced or metastatic breast cancer, as detected by an FDA‑authorized test, following recurrence on or after completing adjuvant endocrine therapy. • in combination with trastuzumab, with or without pertuzumab, and endocrine therapy for the maintenance treatment of adult patients with HR-positive, HER2‑positive locally advanced or metastatic breast cancer following induction treatment.

Dosage and administration (summary)

• Recommended starting dose: 125 mg once daily taken with or without food for 21 days followed by 7 days off treatment. • Dosing interruption and/or dose reductions are recommended based on individual safety and tolerability. Recommended Dosage The recommended dosage of IBRANCE is a 125 mg tablet taken orally once daily for 21 consecutive days followed by 7 days off treatment to comprise a complete cycle of 28 days. IBRANCE tablet may be taken with or without food . Advise patients to take their dose of IBRANCE at approximately the same time each day. If the patient vomits or misses a dose, an additional dose should not be taken. The next prescribed dose should be taken at the usual time.

Contraindications

None. None.

Warnings and precautions

• Neutropenia: Monitor complete blood count prior to start of IBRANCE therapy and at the beginning of each cycle, as well as on Day 15 of the first 2 cycles, and as clinically indicated. ( 2.2 , 5.1 ) • Interstitial Lung Disease (ILD)/Pneumonitis: Severe and fatal cases of ILD/pneumonitis have been reported. Monitor for pulmonary symptoms of ILD/pneumonitis. Interrupt IBRANCE immediately in patients with suspected ILD/pneumonitis. Permanently discontinue IBRANCE if severe ILD/pneumonitis occurs. • Embryo-Fetal Toxicity: IBRANCE can cause fetal harm.

Pregnancy

Pregnancy Risk Summary Based on findings from animal studies and its mechanism of action, IBRANCE can cause fetal harm when administered to a pregnant woman . There are no available data in pregnant women to inform the drug-associated risk.

Storage and supply

Store at 20°C to 25°C (68°F to 77°F); excursions permitted between 15°C to 30°C (59°F to 86°F) . Store in the original blister pack.

Source: Palbociclib (Ibrance) — US FDA prescribing information, 2026-07-06, DailyMed. Summarised and shortened; the full label governs. Iranian registration, indications and labelling may differ.