Afatinib (CAS: 439081-18-2; Formula: C₂₄H₂₅ClFN₅O₃) is a small-molecule, irreversible tyrosine kinase inhibitor targeting the ErbB family (EGFR, HER2, HER4). It is used as an active pharmaceutical ingredient (API) in the development and manufacturing of medications for treating non-small cell lung cancer (NSCLC) with specific epidermal growth factor receptor (EGFR) mutations, particularly exon 19 deletions or exon 21 (L858R) substitutions. By blocking signaling pathways that drive cancer cell proliferation and survival, afatinib is indicated as a first-line therapy for advanced or metastatic EGFR-mutated NSCLC. This product is supplied as an off-white powder with high purity (>98.5%), suitable for pharmaceutical and research applications. The formulated medication is administered orally as tablets once daily. Common adverse effects in clinical use include diarrhea, rash, and stomatitis, managed supportively. Monitoring and dose adjustments are recommended for therapeutic optimization.