Internal Medicine

Lung Cancer

Cellular Transformation in the Airways

Amos Asamoah
October 2025
6 min read
Other Topics

We're completing our respiratory diseases section with lung cancer - the leading cause of cancer-related mortality worldwide. Lung cancer represents a group of malignancies arising from the respiratory epithelium, with diverse histological subtypes and clinical behaviors. I'll guide you through the major classifications, risk factors, diagnostic approaches, staging systems, and evolving treatment paradigms. Understanding lung cancer is crucial as early detection and targeted therapies are transforming outcomes. Let's explore this complex field where oncology meets pulmonary medicine!

🩺 Epidemiology and Risk Factors

Lung cancer incidence and mortality patterns reflect complex interactions between environmental exposures, genetic susceptibility, and demographic factors.

Key Epidemiological Facts

  • Leading cause of cancer death worldwide
  • ~2.2 million new cases annually
  • ~1.8 million deaths annually
  • 5-year survival: ~20% overall
  • Incidence decreasing in men, plateauing in women

Major Risk Factors

  • Tobacco smoking: 85-90% of cases
  • Radon exposure: Second leading cause
  • Occupational exposures: Asbestos, silica
  • Air pollution: PM2.5, diesel exhaust
  • Family history: Genetic predisposition
Risk Factor Relative Risk Key Pathogens/Carcinogens Prevention Strategies
Active Smoking 10-30 fold increase Polycyclic aromatic hydrocarbons, nitrosamines Smoking cessation, public health campaigns
Secondhand Smoke 1.2-1.3 fold increase Same as active smoking, lower dose Smoke-free policies, education
Radon Gas 1.1-1.2 fold increase Alpha particle radiation Home testing, ventilation systems
Occupational Variable (2-50 fold) Asbestos, arsenic, chromium, nickel Workplace safety, protective equipment
Clinical Pearl: Remember that 10-15% of lung cancers occur in never-smokers, and these often have distinct molecular profiles and better responses to targeted therapies.

🔄 Classification and Pathophysiology

Lung cancer classification has evolved from simple small cell vs non-small cell to complex molecular subtypes that guide treatment selection.

Non-Small Cell Lung Cancer (NSCLC)

  • 85% of all lung cancers
  • Adenocarcinoma (40%)
  • Squamous cell (25%)
  • Large cell (10%)
  • Better prognosis than SCLC

Small Cell Lung Cancer (SCLC)

  • 15% of lung cancers
  • Strong smoking association
  • Rapid growth, early metastasis
  • Responsive to chemotherapy
  • Poor long-term survival

Molecular Pathogenesis

  • Field cancerization concept
  • Multiple genetic alterations
  • Driver mutations (EGFR, ALK, KRAS)
  • Epigenetic changes
  • Tumor microenvironment
Tutor Tip: Think of NSCLC as more heterogeneous but generally slower-growing, while SCLC is aggressive with early dissemination - this fundamental difference drives distinct treatment approaches.

👨‍⚕️ Clinical Presentation

Lung cancer symptoms reflect local tumor effects, regional spread, distant metastases, and paraneoplastic syndromes. Many patients present with advanced disease.

Common Presenting Symptoms

Local/Regional Effects

  • Cough (new or changed character)
  • Hemoptysis
  • Chest pain
  • Dyspnea
  • Wheezing/stridor
  • Post-obstructive pneumonia

Metastatic Symptoms

  • Bone pain (bone metastases)
  • Neurological symptoms (CNS mets)
  • Jaundice (liver metastases)
  • Supraclavicular lymphadenopathy
  • Weight loss, fatigue

Paraneoplastic Syndromes

Syndrome Associated Cancer Key Features Mechanism
SIADH SCLC Hyponatremia, euvolemia ADH or ADH-like hormone secretion
Eaton-Lambert SCLC Proximal muscle weakness Autoantibodies to voltage-gated calcium channels
Hypercalcemia Squamous cell Confusion, polyuria, stones PTHrP secretion
Cushing's Syndrome SCLC, carcinoid Hypokalemia, hyperglycemia ACTH or ACTH-like hormone production
Hypertrophic Osteoarthropathy Adenocarcinoma Clubbing, joint pain Unknown, possibly VEGF-mediated
Oncologic Emergencies: Superior vena cava syndrome, spinal cord compression, massive hemoptysis, hypercalcemia, and symptomatic brain metastases require immediate intervention.

🔍 Diagnostic Approach

Lung cancer diagnosis involves imaging for detection and characterization, tissue sampling for histology, and molecular testing for treatment selection.

Diagnostic Pathway

Modality Purpose Key Findings Limitations
Chest X-ray Initial detection Solitary pulmonary nodule, mass, effusion Poor sensitivity for small lesions, lymph nodes
CT Scan Characterization, staging Size, location, lymph nodes, metastases Radiation exposure, false positives
PET-CT Staging, treatment response Metabolic activity, distant metastases False positives (inflammation), cost
Bronchoscopy Tissue diagnosis Direct visualization, biopsies Limited to central lesions, procedural risks
CT-guided Biopsy Peripheral lesions High diagnostic yield Pneumothorax risk, bleeding
Molecular Testing Treatment selection EGFR, ALK, ROS1, BRAF, other mutations Tissue requirements, turnaround time
Important: Always obtain adequate tissue for both histopathological diagnosis and molecular testing. Small biopsies may need to be prioritized for molecular studies in advanced disease.

📊 Staging and Prognosis

Accurate staging using the TNM system is essential for prognosis and treatment planning. Staging differs between NSCLC and SCLC.

TNM Staging System (NSCLC 8th Edition)

Component Description Key Features
T (Tumor) Primary tumor size/invasion T1: ≤3cm, T2: >3-5cm, T3: >5-7cm, T4: >7cm or invasion
N (Nodes) Regional lymph node involvement N1: ipsilateral peribronchial/hilar, N2: ipsilateral mediastinal, N3: contralateral/supraclavicular
M (Metastasis) Distant spread M1a: contralateral lung/pleura, M1b: single extratoracic, M1c: multiple extratoracic

Stage Grouping and Survival

Early Stage (I-II)

  • Stage IA: 5-year survival ~90%
  • Stage IB: 5-year survival ~85%
  • Stage IIA: 5-year survival ~70%
  • Stage IIB: 5-year survival ~60%
  • Treatment: Surgery ± adjuvant chemo

Advanced Stage (III-IV)

  • Stage III: 5-year survival ~30%
  • Stage IV: 5-year survival ~5%
  • Treatment: Multimodal, palliative focus
  • New therapies improving outcomes
Treatment Principle: Stage I-II: Curative intent with surgery; Stage III: Multimodal therapy; Stage IV: Palliative systemic therapy with focus on quality of life.

💊 Treatment Strategies

Lung cancer treatment has evolved from histology-based to biomarker-driven approaches, with personalized therapy based on molecular characteristics.

Treatment Modalities

Modality Indications Key Approaches Recent Advances
Surgery Early stage NSCLC Lobectomy (standard), segmentectomy, pneumonectomy VATS, robotic surgery, sublobar resections
Radiation All stages, palliative care SBRT for early stage, conventional for locally advanced Proton therapy, IMRT, SABR
Chemotherapy Adjuvant, advanced disease Platinum doublets (cisplatin/carboplatin + agent) Maintenance therapy, metronomic dosing
Targeted Therapy Actionable mutations EGFR inhibitors, ALK inhibitors, other TKIs Next-generation inhibitors, combination approaches
Immunotherapy Advanced NSCLC, selected SCLC PD-1/PD-L1 inhibitors (pembrolizumab, nivolumab) Combination regimens, biomarkers for selection

Molecular Targets and Therapies

Common Targets

  • EGFR: Erlotinib, Osimertinib
  • ALK: Crizotinib, Alectinib
  • ROS1: Crizotinib, Entrectinib
  • BRAF: Dabrafenib + Trametinib
  • NTRK: Larotrectinib, Entrectinib

Treatment Selection

  • PD-L1 expression guides immunotherapy
  • Comprehensive molecular profiling
  • Tissue and liquid biopsy options
  • Clinical trial consideration
  • Sequential therapy strategies
Clinical Insight: Always test for PD-L1 expression and actionable mutations before starting first-line therapy for advanced NSCLC - this dramatically impacts treatment selection and outcomes.

🌱 Screening and Prevention

Lung cancer screening and prevention strategies aim to reduce mortality through early detection and risk factor modification.

Screening Criteria

  • Age 50-80 years
  • 20 pack-year smoking history
  • Current smoker or quit <15 years
  • Annual low-dose CT scan
  • Shared decision-making required

Prevention Strategies

  • Tobacco cessation programs
  • Radon testing and mitigation
  • Occupational exposure reduction
  • Healthy diet and exercise
  • Air quality improvements

Emerging Approaches

  • Risk-based screening models
  • Blood-based biomarkers
  • Breath analysis technologies
  • Chemoprevention trials
  • AI-assisted imaging analysis
Pro Tip: Lung cancer screening reduces mortality by 20% in high-risk populations. Always discuss both benefits (early detection) and harms (false positives, overdiagnosis) with eligible patients.

🧠 Key Takeaways

  • Lung cancer is the leading cause of cancer mortality worldwide
  • Major types: NSCLC (85%) and SCLC (15%) with distinct behaviors
  • Tobacco smoking is the predominant risk factor, but never-smokers also develop lung cancer
  • Presentation varies from asymptomatic to local symptoms, metastases, or paraneoplastic syndromes
  • Diagnosis requires imaging, tissue sampling, and molecular profiling
  • Staging determines prognosis and treatment approach
  • Treatment has evolved to include targeted therapy and immunotherapy alongside traditional modalities
  • Screening with low-dose CT reduces mortality in high-risk populations

🧭 Conclusion

We've completed our comprehensive journey through lung cancer, student—from epidemiology and risk factors to the revolutionary advances in targeted therapies and immunotherapy. Remember that lung cancer management requires a multidisciplinary approach and personalized treatment strategies based on histology and molecular profiling. I encourage you to understand the importance of molecular testing and the rapid evolution of treatment options in this field. Excellent work completing the respiratory diseases section! Next, we'll move to gastrointestinal diseases, starting with peptic ulcer disease.

In lung cancer care, personalized medicine has transformed outcomes - the right treatment for the right patient at the right time.

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