Malignant melanoma

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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.
    • Serous carcinoma - both serous carcinoma and melanoma have a large nucleolus.
  • Sarcoma - as may have spindle cells.
  • Lymphoma.
  • Other melanocytic lesions.

Notes:

  • Can look almost like anything.
    • Like it is said that sarcoidosis is in every internal medicine DDx... melanoma is every pathologic DDx.

Electron microscopy

  • Melanosomes.

Image(s):

Stains

  • Fontana-Masson stain, stains melanin.[1]
    • 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.[2]
    • 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

References

  1. URL: http://education.vetmed.vt.edu/curriculum/VM8054/labs/Lab2/Examples/exfontana.htm. Accessed on: 5 May 2010.
  2. Ramos-Herberth FI, Karamchandani J, Kim J, Dadras SS (September 2010). "SOX10 immunostaining distinguishes desmoplastic melanoma from excision scar". J. Cutan. Pathol. 37 (9): 944–52. doi:10.1111/j.1600-0560.2010.01568.x. PMID 20653825.