Tucatinib/tocatinib is an oral tyrosine kinase inhibitor targeting HER2 protein, which is particularly suitable for the treatment of HER2 positive breast cancer patients with brain metastasis. By combining trastuzumab and capecitabine, it significantly improves the survival benefits of patients who have previously received anti-HER2 treatment, including brain metastasis control.

1. Indications and mechanisms of action

(1) Indications: approved for unresectable or metastatic HER2 positive breast cancer (including brain metastasis), trastuzumab and capecitabine should be combined, and patients should have received anti HER2 treatment in the past.

(2) Target: Selective inhibition of HER2 tyrosine kinase, blockade of PI3K-AKT/MAPK pathway, inhibition of tumor growth and induction of apoptosis, good blood-brain barrier penetration.

2 Treatment plan and dosage

(1) Standard protocol: 300mg orally twice daily, combined with trastuzumab (6mg/kg every 21 days) and capecitabine (1000mg/m2 twice daily, days 1-14).

(2) Brain metastasis adjustment: No special dose adjustment is required, but close monitoring of neurological symptoms and imaging changes is necessary.

3 Adverse Reaction Management

(1) Common side effects: diarrhea (80%), hand foot syndrome (63%), nausea (58%), most of which are grades 1-2.

(2) Specific risks of brain metastasis: headache (27%), dizziness (15%), which need to be differentiated from brain edema or progression.

4 Medication precautions

(1) Do not use strong CYP3A inducers or CYP2C8 inhibitors in combination, and avoid CYP3A substrate drugs.

(2) Child Pugh C should be reduced to 200mg twice a day and liver enzymes should be monitored regularly.