A 65-year-old woman with fair skin and history of chronic sun exposure presents with a slowly enlarging, asymmetric brown macule with irregular borders on her left forearm. Biopsy confirms melanoma. Which is the most common site of cutaneous melanoma in Indian patients?

Explanation

## Most Common Site of Cutaneous Melanoma in Indian Patients **Key Point:** In Indian patients (and other individuals with darker skin phototypes), **palms and soles** are the most common sites for cutaneous melanoma, due to the predominance of **Acral Lentiginous Melanoma (ALM)** in this population. ### Melanoma Subtype Distribution by Ethnicity | Subtype | Most Common Site | Caucasians | Indians/Asians/Africans | |---------|-----------------|------------|------------------------| | **Superficial Spreading (SSM)** | Trunk, back | ~70% | ~20–30% | | **Acral Lentiginous (ALM)** | Palms, soles, nail beds | 2–5% | **35–60%** | | **Nodular** | Trunk, head | ~15% | ~15% | | **Lentigo Maligna** | Face, neck | ~5–10% | ~5% | ### Why Palms and Soles Are Most Common in Indians 1. **Acral lentiginous melanoma (ALM)** is the predominant subtype in darker-skinned populations (Fitzpatrick types IV–VI), including Indians, Africans, and East Asians 2. **UV-independent pathogenesis:** ALM arises through mechanisms distinct from UV-induced mutagenesis (e.g., mechanical stress, genetic alterations in KIT), explaining why it predominates in non-sun-exposed acral sites 3. **Relative protection of sun-exposed skin** by melanin in darker phototypes reduces UV-driven melanoma at trunk/back 4. **Multiple Indian studies** (including data from AIIMS, Tata Memorial) confirm acral sites (palms, soles, subungual) account for the majority of melanoma cases in Indian patients 5. **Poor prognosis** of ALM in Indians is partly due to delayed diagnosis — lesions on soles are often mistaken for plantar warts or fungal infections **High-Yield:** In Caucasians, the back/trunk is the most common site (SSM predominates). In Indians and other dark-skinned populations, palms and soles are most common (ALM predominates). This is a classic exam distinction. ### Contrast with Caucasian Patients - **Caucasians:** Back and trunk most common (~30–40%), driven by intermittent UV exposure and SSM subtype - **Indians/Asians/Africans:** Acral sites (palms, soles, nail beds) most common, driven by ALM subtype independent of UV exposure ### Clinical Implications - **Subungual melanoma** (a variant of ALM) is also disproportionately common in Indians — always examine nail beds - **Hutchinson's sign** (periungual pigmentation) is a red flag for subungual ALM - **Delayed diagnosis** is common because acral lesions are often attributed to benign causes; Breslow thickness at presentation is typically greater **Clinical Pearl:** When a question specifies "Indian patients," the answer for most common melanoma site is **palms and soles (acral)**, not the trunk. This reflects the dominance of ALM in darker skin phototypes, as emphasized in Robbins Pathology and multiple Indian dermatology textbooks (IADVL Textbook of Dermatology). [cite: Robbins & Cotran Pathologic Basis of Disease, 10e; IADVL Textbook of Dermatology 4e; Harrison's Principles of Internal Medicine 21e]