## Most Common Histologic Subtype of Cutaneous Melanoma ### Histologic Classification and Prevalence **Key Point:** Superficial spreading melanoma (SSM) is the most common histologic subtype of cutaneous melanoma, accounting for 60–70% of all cases globally, including in Indian populations. ### Comparison of Melanoma Subtypes | Subtype | Frequency | Breslow Thickness at Diagnosis | Prognosis | Key Features | |---------|-----------|--------------------------------|-----------|---------------| | Superficial spreading | 60–70% | 0.75–1.5 mm (intermediate) | Favorable | Radial growth phase, slow progression | | Nodular | 15–20% | 4–8 mm (thick) | Poor | Vertical growth phase dominant, rapid | | Lentigo maligna | 5–10% | 0.6–1.2 mm (thin) | Favorable | Elderly, sun-exposed face, indolent | | Acral lentiginous | 2–10% | 3–4 mm (thick) | Poor | Palms/soles/nails, higher in dark skin | ### Clinical Characteristics of SSM **High-Yield:** SSM typically presents with: - Asymmetry, irregular borders, color variation (ABCDE criteria) - Relatively long radial growth phase (horizontal spread) before vertical invasion - Intermediate Breslow thickness at diagnosis (better prognosis than nodular) - Most favorable 5-year survival among subtypes (~90% for thin lesions) **Clinical Pearl:** The relatively favorable prognosis of SSM compared to nodular melanoma is due to its longer radial growth phase, which allows for earlier detection before deep invasion occurs. **Mnemonic:** **SSM = Slow, Spread, Most common** — Superficial Spreading Melanoma has the slowest growth and most common presentation. ### Why SSM Is Most Common SSM arises from intermittent sun exposure (not chronic like lentigo maligna) and represents the "typical" melanoma in younger to middle-aged adults. Its long radial phase makes it more likely to be detected clinically before becoming thick.
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