Lung Cancer for USMLE Step 2
Lung Cancer for the USMLE Step 2 Exam
Lung Cancer Overview
- Epidemiology:
- Leading cause of cancer-related death worldwide.
- Primarily affects adults over 50, with higher rates among smokers.
- Men are more commonly affected, though incidence in women is rising.
- Risk Factors:
- Smoking: Primary cause, with risk proportional to pack-years.
- Environmental Exposures: Radon, asbestos, secondhand smoke, air pollution.
- Genetic Factors: Family history, genetic mutations (e.g., EGFR, ALK, KRAS).
- History of Lung Disease: Increased risk with chronic obstructive pulmonary disease (COPD), pulmonary fibrosis.
Types of Lung Cancer
- Non-Small Cell Lung Cancer (NSCLC) (~85% of cases):
- Adenocarcinoma: Most common, especially in nonsmokers and women; peripheral lung location.
- Squamous Cell Carcinoma: Central location, linked with smoking, often causes cavitation.
- Large Cell Carcinoma: Poorly differentiated, usually peripheral, and associated with rapid growth.
- Small Cell Lung Cancer (SCLC) (~15% of cases):
- Aggressive, strongly linked to smoking, typically central location.
- Often associated with paraneoplastic syndromes such as SIADH and ectopic ACTH production.
Clinical Presentation
- Respiratory Symptoms:
- Cough: Chronic, nonresponsive to usual treatment.
- Hemoptysis: Often indicates central tumors.
- Dyspnea: Due to airway obstruction, pleural effusion, or significant lung involvement.
- Chest Pain: Persistent, dull, typically worsens with deep breathing or coughing.
- Systemic Symptoms:
- Weight Loss and Anorexia: Common in advanced disease.
- Fatigue: Non-specific, associated with increased tumor burden or anemia.
- Paraneoplastic Syndromes:
- SIADH: Leads to hyponatremia, often seen in SCLC.
- Cushing Syndrome: Due to ectopic ACTH production in SCLC.
- Hypercalcemia: Seen in squamous cell carcinoma due to parathyroid hormone-related peptide (PTHrP) secretion.
- Neurological Syndromes: Lambert-Eaton myasthenic syndrome (proximal muscle weakness) is associated with SCLC.
Diagnostic Evaluation
- Imaging:
- Chest X-ray: Often initial test; may show a mass, nodule, or pleural effusion.
- CT Chest with Contrast: Defines tumor size, lymph node involvement, and metastasis.
- PET-CT: Useful for staging and detecting metastases.
- Biopsy and Pathologic Evaluation:
- Bronchoscopy with Biopsy: For centrally located tumors.
- CT-Guided Needle Biopsy: Preferred for peripheral lesions.
- Sputum Cytology: Non-invasive but limited sensitivity, primarily for central tumors.
- Staging:
- NSCLC (TNM System): Tumor size, nodal involvement, and metastasis determine stage.
- Stage I-II: Early, potentially surgical candidates.
- Stage III-IV: Advanced disease, generally managed with systemic therapy.
- SCLC Staging: Limited (confined to one hemithorax) versus extensive (beyond one hemithorax or distant spread).
Treatment
- NSCLC:
- Surgery: Treatment of choice in early-stage disease without metastasis.
- Radiation Therapy: Used as definitive or palliative treatment, especially in locally advanced cases.
- Chemotherapy: Often platinum-based (cisplatin or carboplatin) for advanced or metastatic disease.
- Targeted Therapy and Immunotherapy: For patients with specific mutations (e.g., EGFR, ALK) or high PD-L1 expression.
- SCLC:
- Chemotherapy: Mainstay treatment; typically platinum-based regimens.
- Radiation Therapy: Used concurrently with chemotherapy in limited-stage disease.
- Prophylactic Cranial Irradiation (PCI): Reduces risk of brain metastasis in patients with complete or partial response to initial treatment.
Key Points
- Lung cancer remains the most common cause of cancer death, with smoking as the most significant risk factor.
- NSCLC includes adenocarcinoma (most common in nonsmokers), squamous cell carcinoma (smoking-related), and large cell carcinoma.
- SCLC is highly aggressive, frequently presenting with paraneoplastic syndromes such as SIADH, Cushing syndrome, and Lambert-Eaton syndrome.
- Diagnosis relies on imaging (initial chest X-ray, followed by CT or PET-CT) and biopsy (bronchoscopy or CT-guided).
- Treatment varies by stage and type: NSCLC may be treated with surgery, radiation, chemotherapy, and targeted agents, while SCLC is primarily managed with chemotherapy and radiation.
- Prognosis is significantly impacted by stage at diagnosis, with early-stage NSCLC offering the best survival outcomes.