Afatinib is primarily used in the treatment of non-small cell lung cancer (NSCLC), particularly in cases where the cancer cells have specific mutations in the epidermal growth factor receptor (EGFR) gene. It is often prescribed for patients with advanced or metastatic NSCLC who have not responded to other treatments. Afatinib works by inhibiting the activity of EGFR and other related proteins, thereby slowing the growth and spread of cancer cells. It is taken orally and is commonly used as a first-line treatment for EGFR mutation-positive NSCLC. Additionally, it may be used in combination with other therapies to enhance its effectiveness in certain cases.