Which melanoma subtype is characterized by a prolonged radial growth phase, typically occurs on sun-exposed areas of the face and neck in elderly patients, and has the best prognosis among all melanoma types?

Explanation

## Lentigo Maligna Melanoma (LMM) **Key Point:** Lentigo maligna melanoma is a melanoma subtype with the longest radial growth phase (often years to decades), lowest metastatic potential, and best overall prognosis among all melanoma types. ### Clinical Features - **Location:** Sun-exposed areas, especially face and neck (photodamaged skin) - **Patient profile:** Elderly patients (typically >60 years) - **Appearance:** Large, irregularly pigmented macule with variegated color (brown, black, red) - **Growth:** Prolonged radial growth phase before vertical invasion ### Prognostic Significance - **5-year survival:** Highest among all melanoma subtypes (>90% for thin lesions) - **Metastatic rate:** Lowest (5–10% overall) - **Breslow thickness:** Often thin at diagnosis due to prolonged radial phase ### Comparison with Other Subtypes | Subtype | Location | Age | RGP Duration | Prognosis | |---------|----------|-----|--------------|----------| | **Lentigo maligna** | Face/neck (sun-exposed) | Elderly (>60) | Years–decades | Best | | Superficial spreading | Trunk, limbs | 30–50 years | Months–years | Intermediate | | Nodular | Any site | 40–70 years | Minimal/absent | Worst | | Acral lentiginous | Palm, sole, nail bed | 50–70 years | Months–years | Poor | **High-Yield:** LMM has the longest radial growth phase and best prognosis; nodular melanoma has the shortest RGP and worst prognosis. **Clinical Pearl:** Lentigo maligna (in situ) can remain stable for years; progression to invasive LMM occurs in only 5–10% of cases. [cite:Robbins 10e Ch 25]