Malignant melanoma

Malignant melanoma, also melanoma, is an aggressive type of skin cancer that can be diagnostically challenging for pathologists.

General

• AKA Malignant melanoma.
• Main DDx: melanocytic lesions - especially if pigmented.
• Known as the great mimicker in pathology; it may look like many things.

Clinical

• ABCD = asymmetric, borders (irregular), colour (black), diameter (large).

Microscopic

Features:

• Classic appearance of melanoma:
  • Loosely cohesive; mix of small nests of cells, single cells.
  • Mixed of spindle and ovoid cell morphology.
  • +/-Occasional large binucleated cells.
  • Cytoplasm: brown pigment (melanin).
  • Prominent (large) red nucleoli (like in serous carcinoma of the ovary).
  • Marked nuclear pleomorphism - variation in cell size, shape & staining (like in serous carcinoma of the ovary).
  • Nuclear pseudoinclusions (like in papillary thyroid carcinoma).

DDx:

• Carcinoma.
  • Esp. serous carcinoma - both serous carcinoma and melanoma have a large nucleolus.
• Sarcoma - as may have spindle cells.
  • Esp. clear cell sarcoma.
• Lymphoma.

Notes:

• Can look almost like anything.
  • Like it is said that sarcoidosis is in every internal medicine DDx... melanoma is every pathologic DDx.
• Melanomas with:
  • An epitheloid cell morphology may mimic adenocarcinoma.
  • A spindle cell morphology may mimic spindle cell carcinoma (squamous cell carcinoma) or a sarcoma.

Electron microscopy

• Melanosomes.

Image(s):

• Melanosomes (nature.com).

Stains

• Fontana-Masson stain, stains melanin.
  • May be useful to differentiate melanin from other brown stuff (e.g. lipofuscin, hemosiderin).

IHC

Standard panel:

• S-100 +ve.
• HMB-45 +ve.
• Melan A (MART-1) +ve.

Others:

• SOX10 +ve -- useful for diff. from excision scar.
  • SOX-10 = pan-schwannian and melanocytic marker.

Notes:

• The standard panel above (S-100, HMB-45, MART-1) is also positive in other lesions, e.g. cellular blue nevus.

See also

• Dermatopathology.
• Dermatologic neoplasms.
• Cytopathology.