Lung Cancer — Causes, Symptoms & Treatment Guide — Symptoms, Causes & Treatment | MyMedicPlus

Lung cancer is the most common cause of cancer-related death worldwide, accounting for approximately 2.2 million new cases and 1.8 million deaths annually — 18% of all cancer deaths. It is classified into two major types: non-small cell lung cancer (NSCLC — 85%), which includes adenocarcinoma (most common, 40%, more common in non-smokers and women), squamous cell carcinoma (30%, strongly associated with smoking), and large cell carcinoma; and small cell lung cancer (SCLC — 15%), which is almost exclusively associated with heavy smoking, is highly aggressive with rapid doubling time, and almost universally metastatic at diagnosis. The 5-year overall survival is approximately 20-25% — reflecting late diagnosis (70% of patients have metastatic or locally advanced disease at presentation). Early-stage (Stage I) lung cancer has 80-90% 5-year survival when resected.

Tobacco smoking is responsible for approximately 85% of lung cancers — the risk increases with pack-years (number of packs per day multiplied by years smoked). Risk begins to fall after cessation but never returns to non-smoker levels. Second-hand smoke (passive smoking) increases lung cancer risk by 20-30%. Radon gas — the second leading cause of lung cancer after smoking — a naturally occurring radioactive gas that seeps into buildings from soil; accounts for 5-15% of lung cancer cases in non-smokers. Asbestos exposure (mesothelioma and lung adenocarcinoma — synergistic with smoking). Air pollution — diesel particulate matter and fine particulate matter (PM2.5) are IARC Group 1 carcinogens for lung cancer. Occupational exposures: arsenic, chromium, nickel, beryllium, diesel exhaust. Genetic/familial factors: EGFR, KRAS, BRAF, ALK, ROS1, and MET mutations identify targetable oncogenic drivers in non-smokers and adenocarcinoma subtypes. Personal history of COPD increases lung cancer risk independent of smoking.

Lung cancer is frequently asymptomatic in early stages — detected incidentally on imaging or via screening. Symptoms when present: persistent or new cough lasting more than 3-4 weeks (the most common initial symptom), haemoptysis (blood in sputum — red flag), unexplained progressive breathlessness, persistent chest or shoulder pain, hoarseness (recurrent laryngeal nerve involvement from left hilar tumours), dysphagia (oesophageal involvement), and recurrent chest infections. Systemic symptoms: unexplained weight loss (over 10% body weight), profound fatigue, anorexia. Metastatic symptoms: bone pain (most common site), headache, focal neurological deficits (brain metastases), jaundice (liver metastases), and lymphadenopathy. Paraneoplastic syndromes are more common in SCLC: SIADH (hyponatraemia), Lambert-Eaton myasthenic syndrome, ACTH secretion causing Cushing's syndrome. Superior vena cava (SVC) obstruction causes facial and neck swelling, headache, and arm oedema — a medical emergency. Horner's syndrome (ptosis, miosis, anhidrosis) from Pancoast (superior sulcus) tumour invasion of the sympathetic chain.

Chest X-ray: initial investigation — shows a pulmonary mass, hilar enlargement, pleural effusion, or lobar collapse. CT chest-abdomen-pelvis with IV contrast: characterises the primary tumour, mediastinal nodes, and distant metastases; guides biopsy planning. PET-CT: best staging modality — identifies occult metastases and guides radiotherapy planning. Tissue biopsy is essential for histological diagnosis and molecular testing: CT-guided lung biopsy, bronchoscopy with biopsy (endobronchial, EBUS-guided), or surgical biopsy (VATS). Molecular profiling (required for NSCLC adenocarcinoma): EGFR mutation (most common actionable mutation — 10-15% of Western cases, 30-50% in East Asian populations), ALK fusion (5%), ROS1 fusion (2%), BRAF V600E (3%), KRAS G12C (13%), MET exon 14 skipping (3%), RET fusion, NTRK fusion, and HER2 mutation. PD-L1 expression by immunohistochemistry determines immunotherapy eligibility. Next-generation sequencing (NGS) of tumour tissue or liquid biopsy (circulating tumour DNA) provides comprehensive molecular profiling. Brain MRI for all Stage III-IV NSCLC and all SCLC to assess for brain metastases. Pulmonary function tests (FEV1, DLCO) assess fitness for surgical resection.

Treatment depends on histology, stage, molecular profile, and performance status. Early NSCLC (Stages I-II): surgical resection (lobectomy or anatomical segmentectomy via VATS or thoracotomy) is the standard of care — achieves cure in 60-80% of Stage I disease. SBRT (stereotactic body radiotherapy) is an effective alternative for medically inoperable patients. Adjuvant osimertinib for 3 years after resection of EGFR-mutated Stage IB-IIIA NSCLC dramatically improves disease-free survival. Locally advanced NSCLC (Stage III): concurrent platinum-based chemoradiotherapy followed by consolidation durvalumab (anti-PD-L1 immunotherapy) — the current standard offering long-term disease control in 25-30%. Metastatic NSCLC (Stage IV) treatment by driver mutation: EGFR-mutated — osimertinib (third-generation EGFR-TKI) first-line; ALK-rearranged — alectinib, brigatinib, or lorlatinib; ROS1-fusion — entrectinib or crizotinib; KRAS G12C — sotorasib or adagrasib; MET exon 14 — capmatinib. No driver mutation — first-line pembrolizumab monotherapy (PD-L1 TPS 50% or above) or pembrolizumab + carboplatin-pemetrexed/paclitaxel combination chemotherapy. SCLC: carboplatin + etoposide + atezolizumab (extensive stage); prophylactic cranial irradiation reduces brain metastasis risk. Palliative radiotherapy for bone pain, brain metastases, and SVC obstruction.

Locally advanced lung cancer causes haemoptysis (massive haemoptysis carries 40% mortality), superior vena cava obstruction (SVCO — facial oedema, arm swelling, dyspnoea — requiring urgent radiotherapy or stenting), pleural and pericardial effusions causing breathlessness and cardiac tamponade, recurrent laryngeal nerve palsy (hoarse voice from mediastinal invasion), and Pancoast syndrome (apical tumour causing arm pain and Horner's syndrome). Brain metastases develop in 40% of non-small cell lung cancer patients. Spinal cord compression from vertebral metastases requires emergency dexamethasone and radiotherapy. Paraneoplastic syndromes (SIADH, Cushing's, Lambert-Eaton myasthenic syndrome) affect 10-15% of lung cancers. Lung cancer remains the leading cause of cancer death globally, killing 1.8 million people annually.

Smoking cessation is the single most effective preventive action — the risk of lung cancer decreases progressively after quitting: 50% reduction after 10 years and continuing to decline. Every cigarette avoided reduces risk. Use smoking cessation support: NRT (patches, gum, inhalers), varenicline (Champix/Chantix — most effective), bupropion. Test homes for radon gas — remediation reduces radon concentrations substantially (sealing floors and improving ventilation); national radon testing programmes exist in many countries. Low-dose CT (LDCT) annual lung cancer screening is recommended for high-risk individuals (50-80 years old with 20 or more pack-year smoking history, currently smoking or quit within 15 years) in the UK, USA, and other countries — reduces lung cancer mortality by 20% (NLST trial) to 26% (NELSON trial). Discuss LDCT eligibility with your GP or pulmonologist if you are a current or ex-heavy smoker.

See a GP urgently if you have any of the following: haemoptysis (blood in cough) — even a single episode requires immediate investigation; a persistent cough lasting more than 3 weeks that is new or changed in a smoker; unexplained progressive breathlessness; unexplained weight loss with chest symptoms; persistent hoarseness; or a chest X-ray showing a lung mass or unexplained pleural effusion. The '2-week wait' (suspected cancer pathway) in the UK means GP referral for urgent CT chest within 2 weeks for suspected lung cancer. Seek emergency care for sudden severe breathlessness (pneumothorax or haemothorax), superior vena cava obstruction (facial swelling, neck vein distension), or acute neurological symptoms (brain metastasis). Eligible patients should ask their GP about lung cancer screening with low-dose CT.