Plasmacytoid
melanoma is an unusual variant of
malignant melanoma. The plasmacytoid morphology can be found in a variety of other
malignancies including
carcinomas,
plasma cell neoplasms,
lymphoproliferative disorders, and
sarcomas. The authors report a rare case of plasmacytoid amelanotic
malignant melanoma in a 78-year-old man presenting with an enlarging palpable, erythematous mass on his left posterior shoulder. A fine needle aspirate showed atypical findings with single amelanotic cells with high nuclear to cytoplasmic ratio, mono- and multi-nucleation with prominent nucleoli and intranuclear inclusions. Review of the excision and immunohistochemical analysis revealed the malignant plasmacytoid cells stained with
vimentin, S-100, HMB-45, and other staining patterns consistent with
melanoma. Initial evaluation was negative for other sites of disease. However, 4 months later, the patient was noted to have metastatic disease to his lungs and liver. Given that the
tumor was noted to be BRAF V600R mutated, the patient was started on single agent
dabrafenib. The plasmacytoid morphology can be found in a variety of
malignancies.
Melanoma should be considered in the differential diagnosis of any
malignancy presenting with plasmacytoid features.