Desmoplastic melanoma may mimic a cutaneous peripheral nerve sheath tumor: Report of 3 challenging cases

Abstract

Desmoplastic melanoma (DM) and cutaneous malignant peripheral nerve sheath tumors (MPNST) reveal histological and immunohistochemical similarities, including S100 positivity and negative staining for conventional melanocytic markers. We present 3 cases of cutaneous S100-positive spindle cell tumors in elderly patients, in which first findings led to initial misdiagnoses as cutaneous MPNST and benign peripheral sheath nerve tumor (neurofibroma). The identification of adjacent atypical melanocytic hyperplasia in the overlying skin along with tumor cell proliferation, also in the superficial dermis, the neurotropic component and the absence of any relationship between the tumor and a major nerve, pre-existing neural benign tumor or the existence of stigmata suggestive of neurofibromatosis raised consideration of a DM. Careful attention should be paid to the presence of a firm dermal nodule and atypical scar lesions especially in sun-exposed areas (mainly head and neck region) in elderly patients associated with S100-positive spindle cell proliferation, solar elastosis and adjacent atypical melanocytic proliferation. In such cases, the possibility of a DM should be excluded with caution, especially if the tumor reveals a paucicellular morphology resembling various non-melanocytic neoplasms including malignant or benign peripheral sheath nerve tumors.

The 2018 World Health Organization Classification of Cutaneous, Mucosal, and Uveal Melanoma: Detailed Analysis of 9 Distinct Subtypes Defined by Their Evolutionary Pathway

“…71,91 Neurofibromas may express the same IHC markers as DM and have to be distinguished by consideration of the morphologic features reviewed above. 92 Finally, mature and hyperplastic scars may be difficult to distinguish from DM, and conversely occasional examples of DM may mimic a scar. Reactivity for pS100 and Sox10 should distinguish these lesions; however, the staining of occasional cells within scars should not be overinterpreted as evidence of melanoma.…”

Sarcoma and the 100,000 Genomes Project: our experience and changes to practice

“…No modification of clinical management was indicated by these changes. However, this may change as new therapeutic agents continue to be identified, such as for patients with sarcomas harbouring NTRK fusion genes [33], or in cases where melanoma has been misclassified as a MPNST [34].…”

Correlative study of epigenetic regulation of tumor microenvironment in spindle cell melanomas and cutaneous malignant peripheral nerve sheath tumors

“…Significant histomorphologic challenges frequently arise in the distinction between cutaneous malignant peripheral nerve sheath tumor (C-MPNST) and spindle cell melanoma (SCM) on account that both entities display immunopositivity for S100 and typically do not exhibit immunoreactivity for more specific markers of melanocytic differentiation 1 – 3 . Morphologic infidelity further presents diagnostic hurdles in discriminating between C-MPNSTs and certain amelanotic SCMs, particularly in sun-damaged areas of the skin 2 . Rendering the correct diagnosis is crucial as prognosis and patient management are different among these lesions.…”