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Desmoplastic melanoma with sarcomatoid dedifferentiation
Maija Kiuru1, Gregory McDermott, Michael Berger
1*Department of Pathology †Human Oncology and Pathogenesis Program ‡Department of Medicine, Dermatology Service, Memorial Sloan-Kettering Cancer Center, New York, NY.
The American Journal of Surgical Pathology
|March 13, 2014
Summary
This study reports a rare biphenotypic tumor combining desmoplastic melanoma (DM) with a sarcomatoid spindle cell nodule. Genetic analysis confirmed a shared origin, suggesting dedifferentiation of DM rather than a collision tumor, with common NF1 gene mutations found in both components.
Area of Science:
- Dermatopathology
- Oncology
- Genetics
Background:
- Desmoplastic melanoma (DM) is a rare melanoma variant typically found on sun-damaged skin in elderly individuals.
- Pure DM is characterized by fusiform melanocytes in a fibrotic stroma, while mixed DM has higher cell density and less fibrosis.
- Both DM subtypes usually express S100 protein uniformly.
Observation:
- A unique biphenotypic tumor on the scalp of a 66-year-old man presented as a pure DM adjacent to an undifferentiated solid spindle cell nodule.
- Initial biopsy of the spindle cell nodule was misdiagnosed as atypical fibroxanthoma.
- The pure DM component stained positive for S100 and SOX10, whereas the sarcomatoid component showed minimal melanocytic marker expression.
Findings:
- Next-generation sequencing revealed shared chromosomal copy number changes and mutations between the DM and sarcomatoid components.
- These genetic similarities support a diagnosis of DM with sarcomatoid dedifferentiation, rather than a collision tumor.
- Both tumor components harbored mutations in the neurofibromin 1 (NF1) gene.
Implications:
- This case expands the understanding of DM's potential for dedifferentiation into sarcomatoid morphology.
- The findings highlight the importance of comprehensive diagnostic workup, including molecular analysis, for unusual cutaneous neoplasms.
- Identifying shared mutations, particularly in NF1, may offer insights into the pathogenesis and potential therapeutic targets for such biphenotypic tumors.
