LUNG CANCER

✓ Medically ReviewedDISEASEID: MDBT0200🚨 TRIAGE: URGENTICD-10: C34.9

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Definition

CLINICAL DEFINITION

Lung cancer is a malignant neoplasm arising from the epithelial cells of the respiratory tract, primarily the bronchi, bronchioles, or alveoli. It is broadly classified into non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC) based on histological and molecular characteristics. Diagnosis requires histopathological confirmation via biopsy, with staging determining the therapeutic approach and prognosis.

IN PLAIN ENGLISH

Lung cancer is a disease where abnormal cells in the lungs grow out of control and form tumours. It can spread to other parts of the body and is most commonly caused by smoking, though non-smokers can also develop it.

COMMON MISCONCEPTION / WHAT IT DOES NOT MEAN

Lung cancer is NOT synonymous with all pulmonary nodules, as many nodules are benign (e.g., granulomas, hamartomas). It is also distinct from metastatic cancer to the lung, which originates from a primary tumour in another organ (e.g., breast or colon cancer).

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Word Breakdown

lung

=lung (from Old English 'lungen')

cancer

=malignant tumour (from Latin 'cancer', meaning crab)

Literal Meaning: A malignant tumour of the lung

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Abbreviations

NSCLC=Non-Small Cell Lung Cancer — accounts for approximately 85% of cases

SCLC=Small Cell Lung Cancer — aggressive neuroendocrine tumour

EGFR=Epidermal Growth Factor Receptor — key mutational target in NSCLC

ALK=Anaplastic Lymphoma Kinase — targetable gene rearrangement in NSCLC

TNM=Tumour, Node, Metastasis — standard staging system

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Synonyms & Variants

Bronchogenic Carcinoma›Pulmonary Neoplasm›Lung Carcinoma›

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Category-Specific Context

As a Disease, lung cancer encompasses a spectrum of histological subtypes with distinct molecular drivers, clinical behaviours, and treatment paradigms. It is primarily classified into non-small cell lung cancer (NSCLC), which includes adenocarcinoma, squamous cell carcinoma, and large cell carcinoma, and small cell lung cancer (SCLC), a highly aggressive neuroendocrine tumour.

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Clinical Context & Usage

CLINICAL SETTINGS

Oncology ClinicRespiratory Medicine WardThoracic Surgery DepartmentPalliative Care UnitEmergency Department

USAGE & DOCUMENTATION NOTES

Often documented by histological subtype and stage, e.g., 'Stage IV EGFR-mutated adenocarcinoma of the right upper lobe'. Clinicians frequently use abbreviations like NSCLC and SCLC. Performance status (ECOG or Karnofsky) is routinely documented to assess fitness for systemic therapy.

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Primary Causes & Pathophysiology

PATHOPHYSIOLOGY

Lung cancer pathogenesis involves the accumulation of genetic and epigenetic alterations in the respiratory epithelium, leading to uncontrolled cellular proliferation and evasion of apoptosis. Chronic exposure to carcinogens, primarily tobacco smoke, induces field cancerisation and sequential histological changes. In NSCLC, specific driver mutations (e.g., EGFR, KRAS, ALK fusions) activate oncogenic signalling pathways. SCLC is characterised by the near-universal inactivation of TP53 and RB1 tumour suppressor genes, driving rapid proliferation and early metastasis. The tumour microenvironment facilitates immune evasion and angiogenesis, enabling local invasion and distant haematogenous or lymphatic spread.

PRIMARY CAUSES

Tobacco smoking

Inhalation of over 60 known carcinogens (e.g., polycyclic aromatic hydrocarbons, nitrosamines) causes direct DNA damage and mutations in respiratory epithelial cells.

Radon gas exposure

Inhalation of radioactive radon decay products emits alpha particles, causing double-strand DNA breaks in bronchial epithelial cells.

Occupational asbestos exposure

Inhaled asbestos fibres cause chronic inflammation, oxidative stress, and physical interference with mitosis, synergistically increasing risk when combined with smoking.

Air pollution (PM2.5)

Fine particulate matter induces chronic airway inflammation and oxidative stress, promoting oncogenic mutations, particularly in non-smokers with EGFR mutations.

Secondhand smoke

Passive inhalation of sidestream smoke exposes non-smokers to similar, albeit lower, concentrations of carcinogens as active smokers.

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Epidemiology

Prevalence:Lung cancer is the most commonly diagnosed cancer globally (excluding non-melanoma skin cancer) and the leading cause of cancer-related mortality. It accounts for approximately 12-13% of all new cancer cases and 18% of all cancer deaths worldwide.

Age Group:Primarily affects older adults, with the median age at diagnosis typically between 65 and 70 years. It is rare in individuals under 40 years of age.

Sex Predilection:Male

Geographic Distribution:Highest incidence and mortality rates are observed in North America, Europe, and East Asia (particularly China), correlating with historical and current tobacco use patterns and industrial pollution. Lowest rates are generally seen in Africa and South America.

Red Flags & Triage ★

TRIAGE LEVEL

🚨 URGENT

DO NOT MISS — LIFE-THREATENING PRESENTATIONS

Superior Vena Cava (SVC) obstruction in a patient with known or suspected lung mass — raises concern for impending airway compromise or cerebral oedema, requiring urgent oncological evaluation for stenting or radiotherapy.
New-onset neurological deficits or severe back pain in a patient with lung cancer — suggests spinal cord compression or brain metastases, necessitating emergency MRI and corticosteroid administration.

URGENT EVALUATION TRIGGERS

Massive haemoptysis (>200-600 mL in 24 hours) — risk of asphyxiation
Acute stridor or severe dyspnoea — suggests central airway obstruction
Sudden focal neurological deficits or altered mental status — suggests brain metastases or paraneoplastic encephalitis
Unilateral leg swelling with pleuritic chest pain — suggests pulmonary embolism, common in malignancy

Contraindications & Precautions

CONTRAINDICATIONS

Poor performance status (ECOG 3-4) — generally contraindicates aggressive cytotoxic chemotherapy or major surgical resection due to unacceptable toxicity risk
Severe pulmonary impairment (e.g.
FEV1 < 40% predicted) — contraindicates pneumonectomy or extensive lung resection

SPECIAL PRECAUTIONS

Assess renal and hepatic function before initiating platinum-based chemotherapy or targeted therapies to adjust dosing and avoid severe toxicity
Monitor for immune-related adverse events (e.g.
pneumonitis
colitis
hepatitis) in patients receiving immune checkpoint inhibitors
Evaluate for latent tuberculosis or chronic viral hepatitis before starting immunosuppressive systemic therapy

Complications

DOWNSTREAM CLINICAL COMPLICATIONS

Superior Vena Cava (SVC) syndrome — tumour compression or invasion of the SVC causing facial/upper extremity swelling and venous distension
Malignant pleural effusion — accumulation of exudative fluid in the pleural space causing dyspnoea and restricting lung expansion
Post-obstructive pneumonia — infection distal to a bronchial obstruction caused by the tumour
Paraneoplastic syndromes — ectopic hormone production (e.g.
SIADH in SCLC
hypercalcaemia in squamous cell carcinoma) or immune-mediated neurological effects
Spinal cord compression — from epidural metastases
requiring emergency radiotherapy or surgery

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Confused With (LASA & DDx) ★

CLINICAL DIFFERENTIAL DIAGNOSES (DDx)

Pulmonary Tuberculosis

Key Distinguishing Feature: Presents with chronic cough, haemoptysis, and weight loss, but typically features apical cavitary lesions on imaging and positive sputum AFB smear/culture.

Benign Pulmonary Nodule (e.g., Granuloma, Hamartoma)

Key Distinguishing Feature: Often calcified, stable in size over serial imaging (typically >2 years), and lacks spiculated margins or metabolic activity on PET scan.

Metastatic Cancer to the Lung

Key Distinguishing Feature: Usually presents as multiple, well-circumscribed 'cannonball' nodules rather than a primary solitary mass, with a known primary malignancy elsewhere.

Lung Abscess

Key Distinguishing Feature: Presents with fever, productive cough with foul-smelling sputum, and an air-fluid level within a thick-walled cavity on chest X-ray or CT.

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Clinical Pearls

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Adenocarcinoma is the most common histological subtype of lung cancer and the most frequent type found in 'never-smokers'. It typically presents as a peripheral mass and is more likely to harbour targetable driver mutations like EGFR or ALK rearrangements.

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Squamous cell carcinoma typically arises centrally in the major bronchi and is strongly associated with a history of smoking. It is the subtype most frequently associated with paraneoplastic hypercalcaemia due to PTHrP secretion.

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Small cell lung cancer (SCLC) is a highly aggressive neuroendocrine tumour that typically presents with central masses and early, widespread metastasis. It is exquisitely sensitive to initial chemotherapy and radiotherapy, but relapse rates are very high.

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Low-dose CT (LDCT) screening is recommended for high-risk individuals (e.g., heavy smokers aged 50-80 with a significant pack-year history) as it has been shown to reduce lung cancer-specific mortality compared to chest radiography.

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Example Usage & SOAP

CLINICAL SENTENCE

"The patient is a 65-year-old former smoker presenting with a 3 cm spiculated right upper lobe mass on CT, biopsy confirmed as moderately differentiated adenocarcinoma, pending molecular profiling for EGFR and ALK."

IN A SOAP NOTE

S: 68yo M with 40 pack-year smoking history presents with 2 months of progressive dry cough, 5kg weight loss, and mild right-sided chest pain. O: Vitals stable. SpO2 96% on room air. Decreased breath sounds in the right upper zone. No clubbing or lymphadenopathy. CT chest shows a 4.5 cm spiculated mass in the RUL with ipsilateral hilar lymphadenopathy. A: Suspected primary bronchogenic carcinoma, clinical stage IIB (T2b N1 M0). P: Refer to respiratory for bronchoscopy and EBUS-TBNA. Order PET-CT and MRI brain for complete staging. Discuss at multidisciplinary tumour board.

DIFFERENTIAL DIAGNOSIS CONTEXT

Differential for a solitary pulmonary nodule: (1) Primary lung malignancy (adenocarcinoma, squamous cell) — consider if spiculated, growing, or PET-avid; (2) Benign neoplasm (hamartoma, carcinoid) — consider if popcorn calcification or slow growth; (3) Infectious granuloma (TB, histoplasmosis) — consider if endemic area or central calcification; (4) Metastasis from extrapulmonary primary — consider if multiple nodules or known history of melanoma/sarcoma.

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Classifications & Scoring

STAGING SCALE

TNM Staging System (8th Edition)

The international standard for staging NSCLC based on Tumour size/invasion (T), regional lymph Node involvement (N), and distant Metastasis (M). Determines stage groups I through IV.

Scale Reference ↗

STAGING SCALE

Veterans Administration Lung Study Group (VALSG) Staging

Traditionally used for Small Cell Lung Cancer (SCLC), classifying disease as Limited Stage (confined to one hemithorax and encompassable within a single radiation port) or Extensive Stage (disease beyond these boundaries).

Scale Reference ↗

SCORING TOOL

ECOG Performance Status Scale

Assesses a patient's level of functioning and ability to care for themselves (0 to 5). Crucial for determining fitness for chemotherapy, surgical resection, and clinical trial eligibility in lung cancer.

Clinical Calculator ↗

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Prognosis

SHORT-TERM OUTCOME

Highly variable and dependent on stage and performance status. Early-stage disease treated with curative intent (surgery or stereotactic radiotherapy) has excellent short-term survival. Advanced metastatic disease has a median short-term survival measured in months without effective systemic therapy.

LONG-TERM PROGNOSIS

The overall 5-year survival rate globally remains low (approximately 15-20%), but has improved significantly for advanced NSCLC with targetable driver mutations (e.g., EGFR, ALK) or high PD-L1 expression treated with immunotherapy. Localised disease has a 5-year survival rate exceeding 60%.

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References & Coding

ICD-10 DIAGNOSTIC CODE

C34.9

LITERATURE CITATIONS & GUIDELINES

[1]Thai AA et al. Lung cancer. Lancet. 2021;398(10311):1245-1265.

[2]Postmus PE et al. Early and locally advanced non-small-cell lung cancer (NSCLC) in adults: ESMO Clinical Practice Guidelines for diagnosis, treatment and follow-up. Ann Oncol. 2017;28(Suppl 4):iv1-iv21.

[3]Planchard D et al. Metastatic non-small cell lung cancer: ESMO Clinical Practice Guidelines for diagnosis, treatment and follow-up. Ann Oncol. 2018;29(Suppl 4):iv192-iv237.

MEDICAL DISCLAIMER — This content is intended for educational purposes and qualified healthcare professionals only. Always refer to current clinical diagnostic criteria, institutional protocols, and official guidelines. Medobo is not responsible for clinical decisions made based on this content.