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

Primary cutaneous and mucosal melanoma shows a wide histological spectrum. The correct diagnosis depends on 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 likely underrecognized and underreported. These often large and frequently ulcerated tumours affect adults and show a wide anatomical distribution including mucosal sites, although there is predilection for sun-damaged skin of the head and neck. Histologically, the tumours are biphasic and contain a pre-existing conventional melanoma. The dedifferentiated component closely resembles atypical fibroxanthoma, both morphologically and immunohistochemically. Transdifferentiated 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 on 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
JournalHistopathology
Early online date5 Jan 2022
DOIs
Publication statusE-pub ahead of print - 5 Jan 2022

Keywords

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

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