Melanocytic nevus
- Melanocytic nevus (mole) is a benign cutaneous tumor composed of pigment-producing nevus cells derived from melanocytes.
- Histopathology: well-nested melanocytic proliferations at the dermal-epidermal junction
Common acquired melanocytic nevus
- Definition: an acquired melanocytic nevus that arises from clusters of melanocytic nevus cells in the epidermis and dermis and manifests as a uniformly pigmented lesion
- Epidemiology: common regardless of age, gender, or ethnicity
- Clinical features
- Most commonly on sun-exposed areas
- Uniform in color and shape
- Stages
- Junctional nevus
- Uniformly brown-black macule with a flat smooth, hairless surface and well-demarcated border
- Grows at the dermal-epidermal junction during childhood
- Uniformly brown-black macule with a flat smooth, hairless surface and well-demarcated border
- Compound nevus
- Uniformly brown-black, dome-shaped elevated papule or nodule with a smooth or verrucous surface; hair may be present
- Arises from a junctional nevus and extends to the dermis after childhood
- Uniformly brown-black, dome-shaped elevated papule or nodule with a smooth or verrucous surface; hair may be present
- Dermal nevus
- Uniformly brown-black, dome-shaped elevated nodule with a smooth or verrucous surface; can become fibrotic over time and hair may be present
- Arises from a compound nevus in the dermis in adults
- Uniformly brown-black, dome-shaped elevated nodule with a smooth or verrucous surface; can become fibrotic over time and hair may be present
- Junctional nevus
| Feature | Melanocytic Nevus (Benign Mole) | Melanoma (Malignant) |
|---|---|---|
| Asymmetry | Symmetrical | Asymmetrical |
| Border | Regular, well-demarcated | Irregular, notched, poorly defined |
| Color | Uniform (tan, brown, black) | Variegated (multiple shades, red, white, blue, black) |
| Diameter | Usually <6 mm | Often >6 mm (but can be smaller, esp. early) |
| Evolving | Stable, unchanging over time | Changing in size, shape, color, or new symptoms |
| Symptoms | Usually asymptomatic | May itch, bleed, ulcerate, or be painful |
| Growth | Slow, predictable growth; may stop | Rapid, erratic growth (radial and/or vertical phase) |
| Histology | Nests of uniform melanocytes at D-E junction &/or dermis; maturation w/ depth; no/rare mitoses; no significant atypia | Atypical melanocytes, pleomorphism, prominent nucleoli, high N/C ratio, increased/atypical mitoses, lack of maturation w/ depth, pagetoid spread (upward epidermal migration) |
| Cellular Atypia | Minimal to none | Present, often significant |
| Mitotic Activity | Rare, typical if present | Often present, can be atypical |
| Metastatic Pot. | None | High, esp. w/ ↑ Breslow depth (vertical growth) |
| BRAF Mutation | Can be present (esp. in acquired nevi) | Common (~50%), target for therapy (e.g., Vemurafenib) |
| S-100 | Positive | Positive |
| HMB-45 | Variable, often positive in junctional component | Often positive |
| Prognosis | Excellent | Variable; depends on stage, Breslow depth, ulceration, nodal status |
| Origin | Benign proliferation of melanocytes | Malignant transformation of melanocytes; can arise de novo or from pre-existing nevus |