## Diagnosis: Lentigo Maligna Melanoma (LMM) ### Clinical Presentation **Key Point:** Lentigo maligna melanoma is characterized by a prolonged radial growth phase (RGP) in the epidermis before dermal invasion, resulting in earlier detection and thinner lesions at presentation. ### Histopathological Features - Atypical melanocytes predominantly in basal layer (intraepidermal) - Minimal dermal component at diagnosis - Lentigo maligna (LM) precursor phase: RGP can last years to decades - When dermal invasion occurs → LMM ### Prognostic Advantage: Breslow Thickness | Melanoma Subtype | Median Breslow Thickness | RGP Duration | 5-Year Survival (Localized) | |------------------|--------------------------|--------------|-----------------------------| | **Lentigo Maligna** | <1 mm (often <0.5 mm) | Years–decades | 90–95% | | **Superficial Spreading** | 0.5–1.5 mm | Months–years | 85–90% | | **Nodular** | >1.5 mm (often >2 mm) | Minimal/absent | 70–80% | | **Acral Lentiginous** | >2 mm (often >3 mm) | Months–years | 60–70% | ### Why LMM Has Better Prognosis 1. **Prolonged RGP** → slow horizontal spread in epidermis → longer window for clinical detection 2. **Thin at diagnosis** → lower Breslow thickness → lower risk of lymph node/distant metastasis 3. **Early detection** → more likely to be excised before deep dermal/subcutaneous invasion **Clinical Pearl:** Lentigo maligna on the face of an elderly patient is often called "melanoma in situ" or "in-situ LMM" when confined to epidermis—these have excellent prognosis with surgical excision alone. **High-Yield:** LMM has the BEST prognosis among invasive melanomas specifically because the RGP phase allows detection at thin, early-stage disease. Nodular melanoma has the WORST prognosis because it skips the RGP and invades deeply from onset. ### Mnemonic: **LMM = Long, Slow, Spotted** (long RGP, slow growth, spotted on face) 
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