Hertab 250mg is an anti-cancer tablet containing Lapatinib, used to treat advanced or metastatic breast cancer, especially HER2-positive types, by blocking cancer cell growth, often with other drugs like Capecitabine. It works by inhibiting HER2 protein, slowing cancer spread, and relieving symptoms like lumps or nipple discharge, but common side effects include diarrhea, nausea, fatigue, skin issues, and potential heart/liver concerns, requiring careful monitoring.