## Diagnosis: Lentigo Maligna Melanoma (LMM) ### Clinical and Pathological Features of LMM **Key Point:** Lentigo maligna melanoma is characterized by a **prolonged radial growth phase (10–20 years) on sun-exposed areas of the face and neck**, which paradoxically results in **earlier detection and better prognosis** compared to other subtypes, despite being a melanoma. ### Why This Patient Has LMM 1. **Location:** Face (cheek) — the classic site for LMM 2. **Age:** 72 years — elderly patient with chronic sun exposure 3. **Duration:** 15-year history of slow growth — consistent with the radial phase of lentigo maligna 4. **Appearance:** Flat, mottled brown patch with ill-defined borders — classic for lentigo maligna 5. **Dermoscopy:** Lacy reticular pattern — pathognomonic for lentigo maligna 6. **Thickness:** 0.8 mm (thin) — detected early due to the prolonged visible radial phase 7. **No ulceration, no mitotic figures** — favourable features ### Comparison of Melanoma Subtypes and Prognosis | Feature | SSM | Nodular | LMM | Acral | | --- | --- | --- | --- | --- | | **Radial phase duration** | 1–5 years | None (vertical from start) | 10–20 years | Variable | | **Typical site** | Trunk, extremities | Trunk, head | Face, neck (sun-exposed) | Palms, soles, nails | | **Age at diagnosis** | 40–60 years | 40–60 years | 60–80 years | 50–70 years | | **Thickness at diagnosis** | Intermediate (0.75–1.5 mm) | Thick (often >4 mm) | Thin (often <1 mm) | Thick (often >3 mm) | | **5-year survival (Stage IB)** | ~90% | ~70% | ~95% | ~60% | | **Prognostic advantage** | Moderate | Poor | **Best** (thin + early detection) | Worst | **High-Yield:** LMM has the **best prognosis of all melanoma subtypes** because the prolonged radial growth phase on a visible area (face) allows detection at a thin, early stage. The 15-year history in this patient is typical. ### The Paradox of LMM **Clinical Pearl:** Although lentigo maligna melanoma is a true melanoma (with invasion into dermis), it is often detected at a thinner stage than superficial spreading melanoma because: - The radial phase is visible and slow (10–20 years) - Patients and physicians are more likely to notice changes on the face - The lesion is on a sun-exposed, frequently examined area - Breslow thickness is often <1 mm at diagnosis ### Dermoscopic Pattern The **lacy reticular pattern** (also called "network pattern") seen on dermoscopy is highly suggestive of lentigo maligna and helps distinguish it from SSM, which shows irregular streaks and dots. ### Why This Is NOT Other Subtypes **Superficial spreading melanoma:** While SSM can occur on the face, the 15-year stable history is atypical. SSM typically has a 1–5 year radial phase. The lacy reticular dermoscopic pattern is more consistent with LMM. **Nodular melanoma:** Nodular melanoma lacks a radial phase and is typically thick (>4 mm) at diagnosis. This patient's thin lesion (0.8 mm) and long history rule out nodular melanoma. **Acral lentiginous melanoma:** Acral melanomas occur on palms, soles, or nails — not on the face. They carry a poor prognosis due to thick presentation and acral location. ### Prognostic Staging This patient has: - **Breslow thickness:** 0.8 mm - **Clark level:** II (dermis) - **No ulceration** - **No mitotic figures** This corresponds to **AJCC Stage IA** (thickness <0.8 mm) or **Stage IB** (thickness 0.8–1.0 mm with no ulceration), with a **5-year survival >95%**. **Mnemonic for LMM: "FACE, SLOW, THIN, GOOD"** - **F**ace (or neck) - **A**ged patient (60–80 years) - **C**hronic sun exposure - **E**arly detection (thin at diagnosis) - **S**low growth (10–20 year radial phase) - **L**acy reticular dermoscopy - **O**lder lesion (long history) - **W**ell-differentiated (low mitotic rate) - **T**hin (Breslow <1 mm) - **H**igh survival (95%+) [cite:Robbins 10e Ch 25; AJCC Melanoma Staging 8th Edition] 
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