Abstract

De-differentiated malignant melanoma is extremely challenging to diagnose, as it often fails to display a conventional immunophenotype. We report a 64-year-old male who presented with right neck swelling involving the parotid gland, without improvement on antibiotics. A cutaneous pigmented lesion of the left preauricular cheek was also noted. Excision of the left cheek lesion demonstrated melanoma with mixed epithelioid and spindled morphology. The patient underwent excision of the right neck mass which showed poorly differentiated epithelioid cells involving the salivary gland and one lymph node. Immunohistochemical studies demonstrated strong PRAME positivity, SALL4 positivity, and negativity for S100, SOX10, HMB45, and Melan-A in the tumor cells. A prior fine needle aspiration from the right neck mass was preliminarily diagnosed as “metastatic germ cell tumor.” Metastatic melanomas can rarely express SALL4, and malignant germ cell tumors can express PRAME. To better characterize the neck lesion, molecular studies were performed and revealed a BRAF V600E mutation; further imaging failed to reveal a gonadal lesion, and a diagnosis of metastatic melanoma was rendered. The purpose of this report is to describe a diagnostically challenging case of undifferentiated melanoma involving the parotid gland, and highlight the potential diagnostic pitfalls and importance of a multimodal approach in reaching an accurate diagnosis. It also enhances our understanding of melanoma as a great mimicker and a tumor with various immunophenotypes. The utilization of molecular analysis, together with the clinical history, is helpful in reaching an accurate diagnosis in poorly differentiated tumors that lack conventional immunohistochemical markers of melanoma.