Non-Small Cell Lung Cancer

Detailed Overview

NSCLC is the leading cause of cancer-related death worldwide. Adenocarcinoma is the most common subtype and often occurs in peripheral lung tissue; it is also the most common lung cancer in non-smokers. Squamous cell carcinoma typically arises centrally in the major bronchi and is strongly linked to smoking. NSCLC is characterized by a slower growth rate compared to small cell lung cancer but is frequently diagnosed at an advanced stage. The therapeutic landscape has been revolutionized by targeted therapies (targeting EGFR, ALK, ROS1) and immune checkpoint inhibitors.

Epidemiology & Demographics

Accounts for 85% of the ~230,000 new lung cancer cases in the US annually. Median age at diagnosis is 70 years. Lifetime risk is 1 in 15 for men and 1 in 17 for women.

Etiological Mechanism

Genomic instability in lung epithelial cells primarily caused by carcinogens in tobacco smoke. In non-smokers, driver mutations (e.g., EGFR, ALK, KRAS) play a predominant role.

Primary Causes

Tobacco smoke containing over 60 known carcinogens (e.g., nitrosamines, polycyclic aromatic hydrocarbons). Radon gas exposure is the second leading cause.

• Tobacco Smoking: Accounts for 80-90% of cases. Risk increases heavily with pack-years.
• Radon Exposure: Naturally occurring radioactive gas accumulating in basements; leading cause in non-smokers.
• Asbestos Exposure: Synergistic risk with smoking; also causes mesothelioma.
• Prior Radiation: Mantle radiation for Hodgkin lymphoma increases risk.

Repeated exposure to carcinogens induces DNA damage, causing normal bronchial or alveolar epithelium to undergo metaplasia, dysplasia, and ultimately malignant transformation. Adenocarcinoma arises from alveolar type II pneumocytes or Club cells, often driven by KRAS or EGFR mutations. Squamous cell carcinoma arises from bronchial epithelium undergoing squamous metaplasia, often demonstrating p53 mutations, keratin pearls, and intercellular bridges. Tumors can grow locally to invade the pleura, chest wall, or mediastinum, and metastasize via lymphatics and blood to the brain, bone, liver, and adrenal glands.

Characteristic Clinical Presentation

• Chronic Cough: A new or changing persistent cough, present in up to 70% of patients.
• Hemoptysis: Coughing up blood, more common in central squamous cell tumors.
• Dyspnea: Shortness of breath due to airway obstruction, pleural effusion, or tumor bulk.
• Weight Loss: Unintentional loss of >10% of body weight (cachexia).

Physical Examination Signs

• Decreased breath sounds or dullness to percussion (pleural effusion).
• Clubbing of the fingers (Hypertrophic pulmonary osteoarthropathy).
• Pancoast syndrome (Horner syndrome + shoulder pain from apical tumor).

• Superior Vena Cava (SVC) Syndrome: Compression of the SVC causing facial plethora, neck vein distension, and upper extremity edema.
• Malignant Pleural Effusion: Fluid accumulation compressing the lung causing severe dyspnea.
• Brain Metastases: Causing seizures, headaches, and focal neurologic deficits.

Diagnostic Criteria & Guidelines

Requires tissue biopsy (via bronchoscopy, CT-guided core biopsy, or surgical resection) confirming malignant non-small cell histology, followed by molecular testing (NGS) and staging imaging.

Differential Diagnosis

• Small Cell Lung Cancer
• Pulmonary Tuberculosis
• Metastatic disease from another primary (e.g., colon, breast)
• Benign pulmonary hamartoma

Laboratory Tests & Biomarkers

• Comprehensive Metabolic Panel: Hypercalcemia (PTHrP production, often squamous cell), Elevated Alk Phos (bone mets).
• Molecular Testing (NGS): Detects EGFR, ALK, ROS1, BRAF mutations or high PD-L1 expression (>50%).

Imaging Modalities & Findings

• Low-Dose CT Chest:
• PET/CT:
• MRI Brain:

• Stage I
  Small tumor (<=4 cm) confined to the lung, no lymph nodes (T1-T2a, N0).
• Stage II
  Larger tumor or involvement of ipsilateral peribronchial/hilar nodes (N1).
• Stage III
  Locally advanced tumor invading mediastinal structures or ipsilateral mediastinal nodes (N2).
• Stage IV
  Distant metastasis (e.g., brain, bone, contralateral lung) or malignant pleural effusion.

Second-Line & Adjunctive Therapy

For progression on targeted therapy: switch to next-generation TKI or Platinum doublet chemotherapy. For progression on immunotherapy: Docetaxel 75 mg/m2 IV q3w + Ramucirumab.

Surgical & Procedural Management

Lobectomy via Video-Assisted Thoracoscopic Surgery (VATS) or robotic approach is the gold standard for early-stage disease. Pneumonectomy if required for central tumors.

Recommended Lifestyle Changes

• Immediate smoking cessation to improve treatment tolerance and survival.
• Pulmonary rehabilitation to improve operative candidacy and functional status.
• Nutritional support to counteract cancer cachexia.

Patient Counseling & Advice

Explain that molecular testing takes 2-3 weeks but is crucial to define the optimal therapy for advanced disease. Discuss the potential side effects of immunotherapy, notably autoimmune pneumonitis and thyroiditis.

Follow-Up & Monitoring Schedule

Surveillance CT chest every 6 months for 2-3 years, then annually. Clinical evaluation for late toxicities of therapy.

Preventive Strategies

Smoking cessation. Lung cancer screening with annual Low-Dose CT for adults 50-80 years with >=20 pack-year smoking history who currently smoke or quit within the past 15 years.

Overall 5-year survival is 25%. Stage I is >70%, whereas Stage IV is roughly 5-10% (though improving significantly with targeted and immunotherapies).