Primary Scrotal Melanoma Presenting as a Large, Amelanotic, Exophytic Mass

A 62-year-old man presented with a 1-year history of an increasingly painful, progressively enlarging, nonpigmented, exophytic and ulcerative mass on the right side of his scrotum (Figure 1). Histologic examination of the lesion demonstrated a nodular melanoma extending to the base of the specimen (Figure 2). Results of melan-A staining were strongly positive, and those for pan cytokeratin and CD45 were negative. Positron emission tomography–computed tomography showed diffuse skeletal and liver metastases and his TNM stage was T4b N3 M1c. The tumor was treated for palliation with wide local excision, and the results of subsequent analysis of the tumor for a KIT gene mutation were negative. Unfortunately the patient died soon after the resection from malignant hypercalcemia related to the metastatic disease.

Primary scrotal melanoma is the least common of the primary genitourinary melanomas; we found only 19 described in the literature.^{1 - 3} The most common presentation is a pigmented macule or papule.¹ Less commonly, the lesion presents as an exophytic, ulcerated mass, as was seen in our patient and 2 other previously described cases.^{2 - 3} In all 3 of these cases, the patients were immunocompetent.

Histologic diagnosis and tumor staging of primary scrotal melanoma are done in a fashion similar to other primary cutaneous and epithelial melanomas. Although nearly half of the reported cases of primary scrotal melanoma died of their disease,^{1 - 3} some authors suggest that primary scrotal melanoma may have a more favorable prognosis than other genitourinary malignancies.¹ While this may be true for those tumors presenting as small pigmented macules or papules, it appears that primary scrotal melanomas presenting as a large, exophytic, ulcerative masses have a poor prognosis: our patient and the 2 previously described^{3 - 4} died from their disease within 6 months of diagnosis.

Genetic profiling of melanomas has revealed that KIT gene mutations are present in some cases, particularly in tumors arising in mucosal and acral sites.⁴ Imatinib, a targeted therapy that is used to treat a variety of neoplasms driven by kinase mutations, has recently been reported to be effective in cases of KIT-mutant metastatic melanoma.⁵ We analyzed our patient's melanoma for a KIT gene mutation; to our knowledge, this is the first scrotal melanoma to be tested. Unfortunately, the results of the analysis were negative. Nevertheless, screening for KIT gene mutations in other primary scrotal and genitourinary melanomas should be considered because the presence of a mutation may open up new treatment options for these unusual and otherwise deadly melanomas.

Correspondence: Dr Lillis, Department of Dermatology, Oregon Health and Sciences University, 3303 SW Bond Ave, CH16D, Portland, OR 97239 (jlillis01@gmail.com).

Financial Disclosure: None reported.