adenocarcinoma of the lung

Lung adenocarcinoma is a subtype of non-small cell lung cancer (NSCLC) originating from the glandular epithelium of the respiratory tract, most commonly forming in the peripheral lung parenchyma near the pleura, in contrast to squamous cell carcinoma which is typically central. Histologically, it shows gland formation and mucin production, often with a lepidic growth pattern (formerly bronchioloalveolar carcinoma) in well-differentiated cases; immunohistochemistry is positive for TTF-1 and napsin A. It is strongly associated with smoking but is also the most common lung cancer subtype in never-smokers, especially women and Asian populations. Key molecular drivers include EGFR mutations (more common in never-smokers, Asians, women), ALK rearrangements, ROS1 fusions, and KRAS mutations (more common in smokers) — these are important because they determine eligibility for targeted tyrosine kinase inhibitors (e.g., erlotinib/osimertinib for EGFR, crizotinib for ALK/ROS1). Clinically, patients may present with cough, weight loss, hemoptysis, or symptoms from metastasis (bone pain, neurologic deficits from brain mets, adrenal involvement). Peripheral location means it's less likely to cause obstructive symptoms early but has a propensity for pleural involvement and malignant pleural effusion. Paraneoplastic syndromes include hypertrophic pulmonary osteoarthropathy and, rarely, Trousseau syndrome (migratory thrombophlebitis). Diagnosis involves CT-guided biopsy or bronchoscopy with histopathology and molecular testing. Staging (TNM) determines prognosis and treatment approach, ranging from surgical resection (early stage) to chemotherapy, targeted therapy, or immunotherapy (e.g., PD-L1 inhibitors) in advanced/metastatic disease. Prognosis is generally poor for advanced-stage disease due to early metastatic potential.