A 58-year-old man from Mumbai presents with a 6-month history of a slowly enlarging dark brown patch on his left cheek. On examination, the lesion measures 2.5 cm × 2 cm, has irregular borders with colour variation (brown and black), and is flat. There is no ulceration or bleeding. Dermoscopy shows asymmetric pigmentation with irregular dots and globules. A biopsy reveals melanoma with a Breslow thickness of 1.2 mm and Clark level III invasion. The mitotic rate is 3 per mm². There are no ulceration or regression features. What is the most likely subtype of melanoma?

Explanation

## Clinical Presentation Analysis The patient presents with a slowly enlarging, flat lesion on the **face (cheek)** of a **58-year-old man** with irregular borders and colour variation over 6 months. The key clinical features are: - **Age:** 58 years (older adult) - **Location:** Face/cheek — chronically sun-damaged skin - **Duration:** 6 months of slow, radial growth - **Morphology:** Flat (macular), asymmetric, irregular borders, brown-black colour variation - **Histology:** Breslow thickness 1.2 mm, Clark level III, no ulceration ## Melanoma Subtypes — Comparison | Feature | SSM | LMM | Nodular | Acral | |---------|-----|-----|---------|-------| | **Growth pattern** | Radial then vertical | Prolonged radial (years) | Vertical from onset | Radial then vertical | | **Location** | Trunk/extremities | **Face, ears, neck (elderly)** | Any site | Palm, sole, nail | | **Appearance** | Flat ± nodule | **Large flat macular patch** | Dome-shaped nodule | Pigmented patch/nodule | | **Background** | Intermittent UV | **Chronic sun damage (lentigo maligna)** | Any | Non-sun-exposed | | **Age of onset** | 40–60 years | **> 60 years** | Any age | 50–70 years | | **Prognosis** | Intermediate | Better (slow radial growth) | Worst | Poor (late diagnosis) | ## Why This Is Lentigo Maligna Melanoma (LMM) **Key Point:** LMM arises from **lentigo maligna (Hutchinson's melanotic freckle)**, an in-situ precursor that develops on chronically sun-damaged skin of the **face, ears, and neck** in older individuals. When invasion occurs, it becomes LMM. **High-Yield:** The combination of: 1. **Elderly patient (58 years)** on **chronically sun-exposed facial skin** 2. **Flat (macular) morphology** — LMM remains flat for years before developing a nodular component 3. **Slow growth over months to years** — characteristic prolonged radial growth phase 4. **Irregular pigmentation (brown and black)** — typical of lentigo maligna background 5. **Dermoscopy:** Asymmetric pigmentation with irregular dots/globules on facial skin is consistent with LMM ...is the hallmark presentation of LMM, not SSM. **Why NOT SSM?** Superficial spreading melanoma (SSM) is the most common subtype overall (~70%), but it predominantly occurs on the **trunk (men) and lower extremities (women)** in patients aged 40–60. SSM is NOT the typical subtype for facial lesions in older adults on chronically sun-damaged skin. **Clinical Pearl:** The precursor lesion of LMM — lentigo maligna — can persist for 5–20 years before invasive transformation. A flat, slowly enlarging pigmented patch on the face of an older patient should always raise suspicion for LMM until proven otherwise. (Robbins & Cotran Pathologic Basis of Disease, 10e, Ch. 25; Fitzpatrick's Dermatology, 9e) ## Prognostic Significance With Breslow thickness 1.2 mm (Stage IB), mitotic rate 3/mm², and no ulceration, the 5-year survival is approximately 85–90%. LMM generally has a favourable prognosis relative to other subtypes due to its prolonged radial growth phase and early detection on visible facial skin. [cite:Robbins 10e Ch 25; Fitzpatrick's Dermatology 9e]