Class:
- Oral irreversible tyrosine kinase inhibitor (TKI) targeting HER2, HER1 (EGFR), and HER4 receptors
Mechanism of Action:
- Blocks the intracellular tyrosine kinase domains of HER receptors, inhibiting downstream signaling pathways responsible for tumor cell proliferation and survival.
Indications:
- Extended adjuvant treatment of early-stage HER2-positive breast cancer following trastuzumab-based therapy to reduce the risk of recurrence.
- Under investigation/used in some metastatic HER2-positive breast cancers.
Dosing:
- Oral, typically 240 mg once daily for 12 months.
- Dose reductions required for toxicity.
Common Adverse Effects:
- Diarrhea (very common and potentially severe; prophylaxis with antidiarrheals recommended)
- Nausea and vomiting
- Fatigue
- Hepatotoxicity (monitor liver function)
- Rash
Pharmacist Considerations:
- Educate patients on proactive diarrhea management and importance of antidiarrheal prophylaxis (e.g., loperamide).
- Monitor liver function tests regularly.
- Counsel on adherence to daily oral therapy and managing GI side effects.
- Assess for drug interactions (CYP3A4 substrate).