Used in the treatment of non-small cell lung cancer (NSCLC) with specific epidermal growth factor receptor (EGFR) mutations. It works by irreversibly inhibiting EGFR and HER2 tyrosine kinases, blocking signals that promote tumor growth. Commonly prescribed for patients with metastatic NSCLC who have exon 19 deletions or exon 21 L858R substitution mutations. Also studied in head and neck squamous cell carcinoma. Taken orally, it helps slow disease progression and improve progression-free survival.