USMLE Guide: Melanoma

Introduction

Melanoma is a malignant tumor that arises from melanocytes, the pigment-producing cells in the skin. It is the deadliest form of skin cancer and has the potential to spread to other organs if not diagnosed and treated early. This USMLE guide aims to provide a comprehensive overview of melanoma, its risk factors, clinical presentation, diagnosis, staging, management, and prognosis.

Risk Factors

• Ultraviolet (UV) Radiation Exposure: Excessive sun exposure or tanning bed use increases the risk of developing melanoma.
• Family History: Individuals with a first-degree relative (parent, sibling, child) diagnosed with melanoma have an increased risk.
• Fair Skin: People with fair skin, light hair, and blue eyes are at higher risk due to decreased melanin protection.
• Dysplastic Nevus Syndrome: Presence of multiple atypical moles is associated with an increased risk of melanoma.
• Immunosuppression: Patients with weakened immune systems (e.g., organ transplant recipients, HIV/AIDS) have an increased risk.
• Personal History: Previous melanoma diagnosis increases the risk of developing a new melanoma.

Clinical Presentation

• Asymmetrical Lesions: Melanoma often exhibits irregular shape and borders, differing from benign moles.
• Color Variation: Lesions may have multiple colors (brown, black, red, white, blue) or appear different from surrounding skin.
• Diameter: Melanomas are typically larger than 6 mm in diameter, but can be smaller in some cases.
• Evolution: Changes in size, shape, color, or symptoms (itching, bleeding, crusting) over time are concerning.
• Metastasis: Advanced melanoma may present with symptoms related to distant organ involvement (e.g., lung, liver, brain).

Diagnosis

• Skin Biopsy: Excisional or punch biopsy with an appropriate margin is essential for histopathological evaluation of suspicious lesions.
• Histopathology: Examination of the biopsy specimen by a pathologist determines the presence of melanoma and its characteristics.
• Imaging: Chest X-ray, CT scan, or PET scan may be performed to evaluate for metastatic disease.

Staging

• TNM Classification: Utilizes tumor thickness, ulceration, lymph node involvement, and distant metastasis to determine the stage.
• Breslow Thickness: The depth of invasion measured in millimeters from the granular layer of the epidermis to the deepest point of tumor invasion.
• Clark Level: Describes the depth of tumor invasion within the skin layers (e.g., level I: confined to epidermis, level II: invasion into papillary dermis).

Management

• Surgical Excision: The primary treatment for localized melanoma involves surgical removal with appropriate margins based on tumor thickness.
• Sentinel Lymph Node Biopsy (SLNB): Recommended for intermediate thickness melanomas to assess regional lymph node involvement.
• Adjuvant Therapy: May be considered based on the risk of recurrence (e.g., interferon-alpha, targeted therapies, immunotherapies).
• Metastatic Disease: Treatment options include surgery, radiation therapy, targeted therapies (BRAF inhibitors), and immunotherapies (checkpoint inhibitors).

Prognosis

• Prognostic Factors: Tumor thickness, ulceration, lymph node involvement, and distant metastasis are important predictors of prognosis.
• Five-Year Survival Rate: Varies based on the stage of melanoma:
  • Stage I: >90%
  • Stage II: 60-80%
  • Stage III: 20-50%
  • Stage IV: <10%
• Early Detection: The prognosis significantly improves with early detection and treatment.

Remember, early detection, sun protection, and regular skin examinations are vital in preventing and managing melanoma.

Note: This USMLE guide provides a concise overview of melanoma. For a more detailed understanding, refer to comprehensive textbooks and clinical guidelines.