Lung Cancer

Lung cancer is classified into non-small cell (NSCLC, 85%) and small cell (SCLC, 15%). NSCLC subtypes include adenocarcinoma (most common, 40%), squamous cell carcinoma (25-30%), and large cell carcinoma. Adenocarcinoma harbors actionable molecular drivers in ~60% of cases: EGFR mutations (exon 19 deletion, L858R — respond to osimertinib), ALK rearrangements (respond to alectinib), ROS1, BRAF V600E, KRAS G12C (sotorasib), and MET exon 14 skipping. PD-L1 expression (tumor proportion score) predicts response to immune checkpoint inhibitors (pembrolizumab, nivolumab). TNM staging (8th edition) guides treatment: T (tumor size and invasion), N (lymph node involvement — N0 none, N1 ipsilateral hilar, N2 ipsilateral mediastinal, N3 contralateral), M (metastases). Stage I-II: surgical resection; Stage III: multimodal (chemoradiation ± surgery ± immunotherapy); Stage IV: systemic therapy guided by molecular profiling and PD-L1.