Benign & malignant neoplasms originating from melanocytes. Anatomic sites, microscopic & gross pathomorphology
There are three melanocytic proliferations we will consider:
- Melanocytic Nevi (benign neoplasm)
- Derived from melanocytes, brown, uniformly pigmented with defined borders and papules.
- Nuclei are uniform and round, with low mitotic activity. Only have a cosmetic concern
- Found on skin where there is high sun exposure
- Dysplastic nevus
- Can be sporadic or familial, familial more likely to become malignant.
- Larger and may number in their hundreds. Flat macules raised slightly with pebbly surface and irregular borders.
- Microscopically, show evidence of abnormal growth, with cells replacing the normal basal cell layer and alterations to the surrounding dermis.
- Found in areas on all areas of skin and increase risk of melanoma.
- Melanoma
- Malignant melanocyte growth, intimately linked to sunlight exposure.
- Large variation in pigment, shades of black, brown, red, blue and grey observed. Borders are irregular and notched
- Microscopically, cells grow as poorly formed nests, with vertical and horizontal growth. Metastatic risk increases with increased vertical growth.
Left: melanomas; right: ordinary nevi. Rows top to bottom show A (asymmetry), B (irregular border), C (variegated colour) and D (diameter).
Image: “Melanoma vs normal mole ABCD rule NCI Visuals Online” by Unknown creator; six images merged by User:Stevenfruitsmaak, Public domain, via Wikimedia Commons.
Mnemonic: the ABCDE warning signs that a pigmented lesion may be a melanoma:
- Asymmetry
- Border irregular or notched
- Colour variegated (black, brown, red, blue, grey)
- Diameter over 6 mm
- Evolution: change in size, shape or colour