Lung Cancer: Causes, Symptoms, Diagnosis and Treatment — Overview, Diagnosis & Treatment Options | MyMedicPlus

Lung cancer is the leading cause of cancer death in both men and women worldwide, responsible for approximately 1.8 million deaths annually globally and approximately 127,000 US deaths per year (2023 estimates). Approximately 238,000 new US cases are diagnosed annually. Non-small cell lung cancer (NSCLC) accounts for approximately 85% of cases, with the major histological subtypes being adenocarcinoma (40%, arising from peripheral airway cells, the most common type in never-smokers), squamous cell carcinoma (25-30%, arising from central airway cells, strongly tobacco-associated), and large cell carcinoma (10-15%). Small cell lung cancer (SCLC) accounts for 15% of cases — a high-grade neuroendocrine tumor with rapid doubling time, early hematogenous dissemination, and initial chemosensitivity followed by universally high relapse rates. The molecular revolution has transformed advanced NSCLC treatment: approximately 70% of lung adenocarcinomas harbor potentially targetable molecular drivers — EGFR mutations (15-20% in Western patients, 40-60% in Asian patients), ALK fusions (3-5%), ROS1 fusions (1-2%), KRAS G12C (13%), MET exon 14 skipping (3-4%), RET fusions (1-2%), BRAF V600E (2-3%), and NTRK fusions (less than 1%). Tobacco smoking remains responsible for approximately 85% of all lung cancers.

Cigarette smoking is the dominant cause of lung cancer, accounting for approximately 85% of all cases. The risk increases with smoking intensity (cigarettes per day) and duration (years smoking) — pack-years exposure provides a quantitative risk estimate. The relative risk of lung cancer in heavy smokers is approximately 20-fold compared to never-smokers. Even light or intermittent smoking confers significant risk. Secondhand smoke (passive smoking) exposure causes approximately 3,000 lung cancer deaths annually in US never-smokers. Radon gas — a naturally occurring radioactive gas from uranium decay in soil and rock — accumulates in poorly ventilated basements and is the second leading cause of lung cancer in the US (approximately 21,000 deaths/year), responsible for approximately 10-14% of all lung cancer deaths. Asbestos exposure causes mesothelioma and significantly elevates lung cancer risk, particularly in smokers (synergistic 50-fold risk elevation vs. never-smokers without asbestos exposure). Occupational carcinogens including nickel, chromium, arsenic, beryllium, and diesel exhaust particulates contribute to occupational lung cancer. Air pollution (PM2.5 fine particulates) contributes to lung cancer risk in never-smokers. Genetic predisposition: EGFR, ALK, and ROS1 driver mutations are more common in never-smoker lung adenocarcinoma, suggesting distinct molecular etiology.

Lung cancer is frequently asymptomatic until advanced, accounting for the historically poor prognosis. Pulmonary symptoms include new-onset or changed chronic cough in a smoker, hemoptysis (blood-streaked sputum or frank blood), progressive dyspnea, wheezing (from endobronchial obstruction), and post-obstructive pneumonia (recurrent pneumonia in the same lobe). Central tumors (squamous cell, SCLC) cause endobronchial symptoms earlier; peripheral adenocarcinomas may grow to large size before causing symptoms. Chest pain — dull, aching, or pleuritic — from pleural or chest wall involvement. Hoarseness indicates left recurrent laryngeal nerve compression from mediastinal adenopathy or apical tumor. Superior vena cava (SVC) syndrome (facial plethora, arm swelling, distended neck veins, headache worse on bending forward) from mediastinal node compression. Pancoast (superior sulcus) syndrome: apical tumor invading the brachial plexus (C8-T2) causing ipsilateral shoulder and arm pain (ulnar distribution), Horner syndrome (ptosis, miosis, anhidrosis), and rib/vertebral destruction. Systemic: weight loss, fatigue, anorexia. Paraneoplastic syndromes: SIADH (hyponatremia), hypercalcemia (SCC, PTHrP), Lambert-Eaton myasthenic syndrome (SCLC, anti-VGCC antibodies), digital clubbing, and hypertrophic pulmonary osteoarthropathy.

Low-dose CT (LDCT) screening (annual, in eligible current/former smokers aged 50-80, 20 pack-year history) is recommended by USPSTF 2021 and detects early-stage lung cancer before symptoms develop. For symptomatic or incidental lung masses, CT chest with IV contrast is the primary imaging modality. PET-CT is the most sensitive test for mediastinal nodal staging and identifies occult distant metastases. Tissue acquisition: bronchoscopy with endobronchial biopsy and bronchoalveolar lavage for central tumors; CT-guided percutaneous core needle biopsy for peripheral tumors; endobronchial ultrasound (EBUS)-guided transbronchial needle aspiration (TBNA) for mediastinal nodes. Adequate tissue for comprehensive molecular profiling is essential for advanced NSCLC. AJCC 8th edition TNM staging: Stage I (T1-2, N0): early, potentially curative; Stage II (T1-3, N0-1); Stage III (T1-4, N0-3, locally advanced); Stage IV (any T, any N, M1): metastatic. Molecular testing of advanced/metastatic NSCLC: EGFR exons 18-21 (PCR or NGS), ALK/ROS1 IHC + FISH or RNA fusion panel, BRAF V600E, MET exon 14 skipping, KRAS G12C, RET fusion, NTRK fusion, HER2, PD-L1 TPS (22C3 assay), and tumor mutational burden (TMB). Brain MRI for staging all NSCLC Stage III-IV and any SCLC.

Stage I-II NSCLC: Lobectomy via video-assisted thoracoscopic surgery (VATS) or thoracotomy is the standard of care with curative intent (5-year OS 60-80%). Sublobar resection (segmentectomy) is acceptable for T1a-b lesions under 2 cm. Stereotactic body radiation therapy (SBRT/SABR: 50-54 Gy in 3-5 fractions) achieves local control exceeding 90% for medically inoperable Stage I. Adjuvant osimertinib for 3 years after resection of EGFR-mutated Stage IB-IIIA NSCLC (ADAURA: 83% reduction in recurrence risk). Adjuvant atezolizumab (anti-PD-L1) for Stage II-IIIA NSCLC with high PD-L1 expression (IMpower010). Stage III (locally advanced): Concurrent chemoradiation (carboplatin-paclitaxel plus 60 Gy) followed by durvalumab consolidation for 12 months (PACIFIC trial: 5-year OS 42.9% vs 33.4% with placebo). Stage IV NSCLC with driver mutations: EGFR-mutated: osimertinib 80 mg/day first-line (FLAURA: mPFS 18.9 months); ALK-rearranged: alectinib or lorlatinib (ALEX/CROWN trials: superior CNS activity); ROS1: entrectinib or crizotinib; KRAS G12C: sotorasib or adagrasib; MET exon 14: tepotinib or capmatinib; RET: selpercatinib. Stage IV NSCLC without driver mutations: PD-L1 TPS 50% or greater: pembrolizumab monotherapy (KEYNOTE-024: mOS 26.3 months vs 14.2 months chemo); PD-L1 1-49%: pembrolizumab plus carboplatin-pemetrexed or carboplatin-paclitaxel. SCLC, extensive stage: atezolizumab plus carboplatin-etoposide (IMpower133); durvalumab plus carboplatin-etoposide (CASPIAN).

Five-year overall survival by stage: Stage IA1 (T1a-NSCLC) approximately 90%; Stage IB approximately 73%; Stage IIA approximately 65%; Stage IIIA approximately 36%; Stage IIIB approximately 26%; Stage IV approximately 10%. With targeted therapies for driver mutations, metastatic EGFR-mutated NSCLC achieves median OS of approximately 38 months with osimertinib; ALK-rearranged NSCLC achieves median OS of approximately 7 years with modern ALK TKIs. PD-L1 high (TPS 50% or greater) NSCLC without driver mutations achieves median OS of approximately 26 months with pembrolizumab. Extensive-stage SCLC median OS is approximately 12-13 months with immunotherapy-based first-line regimens; SCLC is rapidly lethal at relapse. The prognosis for Lung Cancer: Causes, Symptoms, Diagnosis and Treatment varies depending on severity at diagnosis, the patient's overall health, and how promptly treatment is initiated. With early diagnosis and appropriate management, many patients achieve good outcomes and maintain quality of life. Regular follow-up with healthcare providers is essential to monitor progress, adjust treatment as needed, and detect any complications early. Adherence to prescribed treatments and lifestyle modifications significantly improves long-term prognosis.

Tobacco smoking cessation is the single most powerful lung cancer prevention measure. Cessation at any age reduces risk: risk begins declining within 5 years and approaches near-never-smoker levels after 25-30 years of abstinence. Pharmacotherapy aids cessation: nicotine replacement therapy, varenicline (Chantix, most effective), bupropion. Radon testing of homes, particularly basements in high-radon geographic areas, followed by radon mitigation (sub-slab depressurization systems) when levels exceed 4 pCi/L (EPA action level), prevents approximately 11,000-14,000 US lung cancer deaths annually. Asbestos abatement with proper protective equipment for all demolition and renovation workers exposed to asbestos-containing materials. Annual LDCT screening (USPSTF 2021 recommendations: age 50-80, 20 pack-year history, current smoker or quit within 15 years) reduces lung cancer mortality by 20-24% in high-risk individuals and is covered by US Medicare and most private insurance. Air quality improvement through PM2.5 pollution control policies reduces population-level lung cancer risk in never-smokers.

Any current or former smoker who develops a new or changed cough, hemoptysis (blood in sputum), chest pain, hoarseness, unexplained weight loss, or progressive shortness of breath should seek prompt evaluation — do not attribute new respiratory symptoms to pre-existing COPD or chronic bronchitis without imaging to exclude lung cancer. Current or former smokers aged 50-80 years with a 20 pack-year smoking history who have not had low-dose CT lung cancer screening should discuss eligibility with their primary care physician and arrange screening — this is a covered preventive service. A new, unexplained, solitary pulmonary nodule discovered incidentally on chest X-ray or CT (performed for another reason) requires follow-up according to Fleischner Society guidelines; do not ignore incidental findings. Shoulder or arm pain combined with drooping eyelid and reduced sweating on the same side of the body (Horner syndrome) in a smoker is a potential Pancoast tumor requiring urgent chest imaging. Any non-smoker who develops respiratory symptoms including persistent cough, hemoptysis, or unexplained dyspnea should also be evaluated promptly, as lung cancer occurs in 15% of patients without smoking history and has specific molecular drivers (EGFR, ALK, ROS1) amenable to targeted therapy.