Thoracic Neoplasms: Histology, Stage, and Biomarkers
Screening
Annual low-dose CT screening is recommended for adults 50–80 years with ≥20 pack-years who currently smoke or quit within 15 years. Screening reduces lung cancer mortality; it does not replace cessation counseling.
Histology and staging
Adenocarcinoma is the most common nonsmall cell histology, often peripheral; squamous cell carcinoma is central and may cavitate; small cell carcinoma is central, rapidly growing, and strongly smoking-related. Staging uses TNM, with mediastinal nodal sampling (EBUS-TBNA or mediastinoscopy) required before surgery when nodes are enlarged or PET-avid. PET-CT can stage but not substitute for tissue. Brain MRI is standard in stage III–IV disease.
Stage-directed therapy
Early NSCLC (stage I–II) is treated with surgical resection, with stereotactic body radiotherapy for medically inoperable patients. Stage III is chemoradiation followed by consolidation durvalumab. Stage IV requires biomarker testing first: EGFR, ALK, ROS1, BRAF, KRAS, and PD-L1. Targeted therapy for driver mutations outperforms chemotherapy and is the exam's preferred answer. Small cell carcinoma is divided into limited (chemoradiation plus prophylactic cranial irradiation) and extensive (platinum plus etoposide plus immunotherapy).
Paraneoplastic and compressive syndromes
Pancoast tumors cause shoulder pain and Horner syndrome; superior vena cava syndrome causes facial swelling and distended neck veins; SIADH and Lambert-Eaton syndrome suggest small cell carcinoma; hypercalcemia suggests squamous cell carcinoma. Malignant mesothelioma links to asbestos and presents with pleural thickening and effusion.
Worked rule
Never start systemic therapy in advanced nonsmall cell lung cancer before driver mutation and PD-L1 results return.