A 58-year-old man presents with a 2-cm dark brown nodule on his left shoulder that has been present for 8 months. He reports recent rapid growth and bleeding. On examination, the lesion is asymmetrical, has irregular borders, and shows variegated pigmentation with areas of black, brown, and red. Dermoscopy reveals a blue-grey veil and atypical vascular patterns. Excision biopsy shows invasion into the subcutaneous fat with a Breslow thickness of 3.2 mm and 8 mitoses per mm². Clark level is IV. What is the most likely melanoma subtype?

Explanation

## Diagnosis: Nodular Melanoma **Key Point:** Nodular melanoma (NM) is characterized by vertical/dermal growth from onset, rapid growth, and poor prognosis due to early deep invasion. ### Clinical Features Pointing to Nodular Melanoma | Feature | Nodular Melanoma | Superficial Spreading | Lentigo Maligna | Acral Lentiginous | |---------|------------------|----------------------|-----------------|-------------------| | **Growth pattern** | Vertical from start | Radial then vertical | Radial (slow) | Radial then vertical | | **Duration** | Months (rapid) | Months to years | Years (slow) | Months to years | | **Appearance** | Nodular, uniform color | Asymmetric, variegated | Flat, tan/brown | Flat or nodular, palms/soles | | **Breslow thickness** | Often >2 mm at diagnosis | Variable | Often <1 mm | Often >2 mm | | **Clark level** | III–V | II–V | II–III | III–V | | **Mitotic rate** | High | Variable | Low | High | **High-Yield:** This patient's 8-month history of rapid growth, nodular appearance, deep invasion (Breslow 3.2 mm, Clark IV), and high mitotic rate (8/mm²) are hallmark features of nodular melanoma. NM accounts for ~15–30% of melanomas but has worse prognosis than superficial spreading melanoma at equivalent thickness. ### Why This Patient Has Nodular Melanoma 1. **Rapid growth** — months, not years 2. **Nodular morphology** — raised, uniform color (not variegated radial growth) 3. **Deep invasion at diagnosis** — Clark IV, Breslow 3.2 mm indicates vertical growth from onset 4. **High mitotic rate** — 8/mm² indicates aggressive biology 5. **Bleeding/ulceration** — sign of advanced dermal invasion **Clinical Pearl:** Nodular melanoma has no true radial growth phase; it grows vertically from the start. This is why it is often diagnosed at a thicker stage and carries a worse prognosis than superficial spreading melanoma at the same thickness. ### Prognostic Factors in This Case - **Breslow thickness 3.2 mm** — Stage IIB–IIC (AJCC 8th ed.) - **Mitotic rate 8/mm²** — High risk (≥1 mitosis/mm² is adverse) - **Clark level IV** — Invasion into subcutaneous fat - **Ulceration status** — Not mentioned, but bleeding suggests potential ulceration **Mnemonic: ABCDE of Melanoma** — Asymmetry, Border irregularity, Color variegation, Diameter >6 mm, Evolution (change). Nodular melanoma may lack the radial phase, so rapid growth and nodular morphology are key red flags. **High-Yield:** Nodular melanoma is the second most common subtype (~15–30%) but accounts for disproportionately high mortality because it is often thicker at diagnosis.