A 42-year-old woman presents with a rapidly enlarging dark nodule on her upper back that has grown over 3 months. On examination, the lesion is 1.5 cm, raised, dark brown to black, with an irregular border and surface ulceration. Dermoscopy shows a homogeneous dark pattern without distinct architectural features. Histopathology reveals a thick lesion (Breslow thickness 4.2 mm) with predominantly dermal and subcutaneous involvement, minimal intraepidermal component, and brisk mitotic activity. What is the most likely subtype, and which prognostic factor is most concerning?

Explanation

## Diagnosis: Nodular Melanoma with Adverse Prognostic Factors ### Clinical and Histopathologic Features of Nodular Melanoma **Key Point:** Nodular melanoma is characterized by rapid growth, a raised/nodular appearance, lack of a significant radial growth phase, and predominantly vertical (dermal/subcutaneous) invasion. ### Why This Case is Nodular Melanoma 1. **Rapid growth:** 3-month history (vs. years for LMM or SSM) 2. **Raised, nodular appearance:** Classic presentation 3. **Minimal intraepidermal component:** Predominantly dermal/subcutaneous invasion 4. **Homogeneous dermoscopic pattern:** Lacks the architectural detail of SSM or reticular pattern of LMM 5. **Ulceration and brisk mitotic activity:** Signs of aggressive behavior ### AJCC Prognostic Factors in Melanoma | Prognostic Factor | Impact on Prognosis | Breslow Thickness Correlation | |-------------------|-------------------|-------------------------------| | **Breslow thickness** | Most important independent predictor | > 4 mm = Stage IIIB/C | | **Mitotic rate** | High rate (≥ 1/mm²) = worse prognosis | Incorporated into T stage | | **Ulceration** | Upstages lesion by one T category | Present in 10–15% of melanomas | | **Clark level** | Less important than Breslow | Mainly historical | | **Lymphovascular invasion** | Associated with worse outcome | Indicates higher risk | **High-Yield:** Breslow thickness > 4 mm is the single most powerful prognostic factor in this case. It places the patient at high risk for lymph node involvement and distant metastasis (5-year survival ~50%). ### Mnemonic for Melanoma Subtypes: **"SLNA"** **S** = Superficial Spreading (most common, intermediate prognosis) **L** = Lentigo Maligna (sun-exposed, best prognosis) **N** = Nodular (worst prognosis, rapid) **A** = Acral Lentiginous (worst prognosis, late diagnosis) ### Why Nodular Melanoma Has Worst Prognosis **Clinical Pearl:** Nodular melanoma lacks a prolonged radial growth phase, allowing rapid invasion into the dermis and subcutis before clinical detection. This results in thick lesions at diagnosis and higher rates of lymph node involvement. ### Breslow Thickness Staging ```mermaid flowchart TD A[Melanoma]:::outcome --> B{Breslow Thickness}:::decision B -->|< 0.8 mm| C[Stage IA]:::outcome B -->|0.8-1.0 mm| D[Stage IB]:::outcome B -->|1.01-2.0 mm| E[Stage IIA]:::outcome B -->|2.01-4.0 mm| F[Stage IIB/IIC]:::outcome B -->|> 4.0 mm| G[Stage IIIB/C]:::urgent G --> H[High risk: SLN biopsy + adjuvant therapy]:::action ``` **Key Point:** A Breslow thickness of 4.2 mm places this patient at Stage IIIB/C and mandates sentinel lymph node biopsy and consideration of adjuvant immunotherapy (interferon or checkpoint inhibitors). [cite:Robbins 10e Ch 25]