Primary dedifferentiated, transdifferentiated and undifferentiated melanomas: overview of the clinicopathological, immunohistochemical and molecular spectrum

Ingrid Ferreira, Mark J Arends, Louise van der Weyden, David Adams, Thomas Brenn

Research output: Contribution to journalArticlepeer-review

Abstract / Description of output

Primary cutaneous and mucosal melanoma shows a wide histological spectrum. The correct diagnosis depends upon the demonstration of melanocytic differentiation by recognition of an associated in-situ component or immunohistochemical evidence of a melanocytic phenotype using conventional melanocytic markers, such as S-100, SOX10, Melan-A and HMB-45. Exceptionally, melanomas lose their melanocytic phenotype, at least focally, and show differentiation towards other lineages. Review of the literature shows that de- and trans-differentiation in melanoma is rare but probably under-recognised and under-reported. These often large and frequently ulcerated tumours affect adults and show a wide anatomical distribution, including mucosal sites, although there is a predilection for sun-damaged skin of the head and neck. Histologically, the tumours are biphasic and contain a pre-existing conventional melanoma. The de-differentiated component closely resembles atypical fibroxanthoma, both morphologically and immunohistochemically. Trans-differentiated melanoma may show rhabdomyosarcomatous or spindle cell carcinomatous features. Undifferentiated melanomas are similar tumours in which the conventional melanoma component is absent. Their diagnosis depends entirely upon the clinical context and identification of a classical melanoma driver gene mutation, i.e. BRAF V600E. The diagnosis of these rare and unusual tumours is challenging, and requires thorough tumour sampling and recognition of the background of a pre-existing but often focal conventional melanoma together with molecular analysis.

Original languageEnglish
Pages (from-to)135-149
JournalHistopathology
Volume80
Issue number1
Early online date5 Jan 2022
DOIs
Publication statusPublished - Jan 2022

Keywords / Materials (for Non-textual outputs)

  • dedifferentiated
  • undifferentiated
  • melanoma
  • atypical fibroxanthoma
  • pleomorphic dermal sarcoma
  • rhabdomyosarcoma

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