A 58-year-old man presents with a slowly enlarging, irregularly pigmented macule on his left cheek that has been present for 3 years. Dermoscopy shows asymmetry, irregular borders, and variable pigmentation. Histopathology confirms melanoma with intraepidermal and dermal components. Which is the most common subtype of cutaneous melanoma?

## Most Common Melanoma Subtype **Key Point:** Superficial spreading melanoma (SSM) accounts for approximately 70% of all cutaneous melanomas, making it the most common subtype globally and in India. ### Epidemiology and Clinical Features | Feature | SSM | Nodular | Lentigo Maligna | Acral Lentiginous | |---------|-----|---------|-----------------|-------------------| | **Frequency** | 70% | 15–20% | 5–10% | 2–3% (higher in darker skin) | | **Age of onset** | 40–50 years | 40–50 years | 60–70 years | 50–70 years | | **Duration before diagnosis** | 1–5 years | Months | Years to decades | Months to years | | **Prognosis** | Intermediate | Worst (vertical growth) | Better (early detection) | Poor (late diagnosis) | | **Common sites** | Trunk, extremities | Any site | Face, neck | Palms, soles, nail beds | ### Clinical Presentation of SSM 1. **Slow horizontal (radial) growth phase** lasting 1–5 years before vertical invasion 2. **Asymmetric, irregularly bordered macule** with mixed pigmentation (brown, black, red, white) 3. **Diameter typically >6 mm** at presentation 4. **Trunk and lower extremities** are most common sites 5. **Relatively better prognosis** than nodular melanoma due to prolonged radial growth phase **High-Yield:** The radial growth phase of SSM allows a longer window for early detection compared to nodular melanoma, which has rapid vertical growth from onset. ### Why SSM is Most Common - Arises from **pre-existing or de novo melanocytic nevi** with intermittent sun exposure history - Affects middle-aged individuals with cumulative UV exposure - More common in fair-skinned populations (Caucasians, Europeans) - In India, SSM remains the most common subtype, though acral lentiginous melanoma has higher relative frequency in darker-skinned populations **Clinical Pearl:** The presence of a radial growth phase with asymmetric borders and color variation in a middle-aged patient on the trunk or extremities is classic for SSM. ### Prognostic Significance - **Breslow thickness** at diagnosis is the strongest prognostic factor - SSM typically detected at intermediate thickness (1–4 mm) due to its slow horizontal growth - **5-year survival** varies with stage: Stage I (>95%), Stage II (50–90%), Stage III (20–70%) [cite:Robbins 10e Ch 25]