A 52-year-old woman presents with a 3 mm dark nodule on her back that has been present for 6 months. Histopathology shows a melanoma with the following features: predominantly dermal invasion, lack of significant junctional component, and absence of sun-damaged skin around the lesion. All of the following statements regarding this melanoma subtype are correct EXCEPT:

Explanation

## Melanoma Subtypes: Clinical and Prognostic Features ### Distribution of Melanoma Subtypes | Subtype | Frequency | Key Features | Prognosis | |---------|-----------|--------------|----------| | **Superficial Spreading (SSM)** | 60–70% | Radial growth phase; junctional component; variable sun exposure | Better (detected earlier) | | **Nodular (NM)** | 15–20% | De novo; minimal/no junctional component; vertical growth | Worse (deeper at diagnosis) | | **Lentigo Maligna (LMM)** | 5–10% | Extensive junctional component; sun-damaged skin; face/neck | Better (often thinner) | | **Acral Lentiginous (ALM)** | 5–10% | Palms, soles, nail beds; high-risk in darker skin | Worse (late detection) | **High-Yield:** Nodular melanoma accounts for **15–20%** of all cutaneous melanomas, NOT 50%. The 50% figure is incorrect and is the trap in this question. **Key Point:** The patient's lesion (3 mm, predominantly dermal, no junctional component, no surrounding sun damage) is classic for **nodular melanoma**. ### Why Nodular Melanoma Has Worse Prognosis 1. **De novo origin**: Arises without a radial growth phase → no early detection window 2. **Vertical growth from onset**: Deeper invasion at presentation 3. **Minimal junctional component**: Less epidermal involvement, more dermal/subcutaneous invasion 4. **Breslow thickness**: Often thicker at diagnosis compared to SSM **Clinical Pearl:** Nodular melanomas are often described as "aggressive" because they grow vertically rather than horizontally. A 3 mm nodular melanoma may have worse prognosis than a 3 mm SSM. ### Distinguishing Features ```mermaid flowchart TD A[Melanoma Subtype]:::outcome --> B{Junctional component present?}:::decision B -->|Yes, extensive| C{Sun-damaged skin?}:::decision C -->|Yes| D[Lentigo Maligna Melanoma]:::outcome C -->|No| E[Superficial Spreading Melanoma]:::outcome B -->|Minimal/Absent| F[Nodular Melanoma]:::outcome A --> G{Acral location?}:::decision G -->|Yes| H[Acral Lentiginous Melanoma]:::outcome ``` **Warning:** Do not confuse frequency with prognosis. Nodular melanoma is LESS common (15–20%) but has WORSE prognosis than SSM (60–70%), which is more common but detected earlier. [cite:Robbins 10e Ch 25]