Lung Cancer

 

Clinical Background

Lung cancer is the leading cause of cancer death in the U.S.

Epidemiology

  • Incidence
    • More than 150,000 new cases annually in the U.S.
  • Age – peak incidence is 55-65 years
  • Sex – M>F
    • Female prevalence has increased; male prevalence has stabilized

Risk Factors

  • Tobacco use
    • 13-fold increase in risk for primary user
    • Secondhand exposure – 1.14 to 5.20 relative risk for people who live/lived with smokers
  • Radon/uranium exposure
  • Asbestos exposure – cumulative risk if patient smokes
  • Previous chest irradiation
  • Genetic – positive family history combined with tobacco use increases the risk

Pathophysiology

  • Any tumor arising from respiratory epithelium or pneumocytes
  • 4 main tumor types (account for 85-90% of all lung cancers)
    • Non-small cell lung cancer (NSCLC) account for 85-90% of all lung cancers
      • Squamous (epidermoid) cell carcinoma (SCC)
      • Adenocarcinoma (includes bronchioloalveolar)
      • Large cell (large cell anaplastic)
    • Small cell lung cancer (SCLC)
  • Remainder of tumors
    • Undifferentiated, carcinoid, bronchial gland tumors, sarcomas
    • Other tumors rare
  • Recent rates of adenocarcinoma are equivalent to squamous cell carcinoma
    • Postulated reasons for change in distribution are the change in tobacco components (less tar in current tobacco products, leading to less squamous cell)

Clinical Presentation

  • 20% of patients are incidentally identified while asymptomatic by a chest x-ray for other reasons
  • Symptoms are related to the following:
    • Local tumor growth
    • Invasion and obstruction of adjacent structures
    • Distant metastases
    • Tumor product secretion
  • Symptoms based on area of tumor growth
    • Central – cough, wheeze, hemoptysis, stridor, dyspnea, postobstructive pneumonia
    • Peripheral – pleural/chest wall pain, cough, dyspnea
    • Invasion and obstruction of adjacent structures
      • Tracheal obstruction – dyspnea, wheezing
      • Esophageal compression – dysphagia
      • Recurrent laryngeal nerve invasion – hoarseness
      • Phrenic nerve invasion – diaphragmatic paralysis
      • Sympathetic nerve invasion – Horner syndrome
        • Ptosis
        • Miosis
        • Enophthalmos
        • Unilateral loss of sweating
      • Invasion of lung apex – pancoast tumor, superior vena caval syndrome
    • Distant metastases
      • Superior vena caval syndrome
      • Pericardial tamponade
      • Pleural effusions
      • Pathologic bone fractures
      • Adrenal insufficiency (rare) 
    • Paraneoplastic syndromes
      • Common; may be first presenting symptoms of lung cancer
      • Endocrine syndromes
        • Ectopic parathyroid hormone
          • Usually squamous cell
          • Hypercalcemia, hypophosphatemia
        • Antidiuretic hormone (ADH)
          • Usually SCLC
          • Syndrome of inappropriate secretion of ADH
          • Hyponatremia
        • Adrenocorticotropic hormone (ACTH)
          • Usually SCLC
          • Usually not Cushingoid in appearance
          • Hypokalemia
      • Skeletal/connective tissue syndromes
        • Clubbing
          • 30% incidence
          • Usually NSCLC
        • Hypertrophic pulmonary osteoarthropathy
          • Usually adenocarcinoma
      • Neurologic/myopathic syndromes
        • Eaton-Lambert syndrome
          • Usually SCLC
          • Myasthenia gravis symptoms
        • Retinal blindness
          • Usually SCLC
        • Peripheral neuropathy
        • Subacute cerebellar degeneration
        • Cortical degeneration
      • Polymyositis
      • Hematologic syndromes
        • Migratory thrombophlebitis – Trousseau sign
        • Nonbacterial endocarditis – marantic endocarditis
        • Disseminated intravascular coagulation
      • Dermatologic syndromes
        • Uncommon
        • Dermatomyositis
        • Acanthosis nigricans
      • Systemic syndromes
        • Unknown etiology
        • Cachexia, anorexia, fever, weight loss, suppressed immunity