Anorectal melanoma and seborrheic dermatitis – A case report

Anorectal melanoma (ARM) is a rare and aggressive neoplasm with predisposition for early infiltration, distant spread, and unfavorable prognosis. It has been speculated that Malassezia yeasts could possibly have an impact on skin carcinogenesis and development of melanoma, especially in patients with seborrheic dermatitis (SD), due to production of aryl hydrocarbon receptor (AhR) agonists.

A 52-year-old man with intensive SD complained of a four-month-long rectal bleeding, tenesmus, pain, and difficulty during defecation. On examination, a rectal tumor was detected and histopathology of tumor tissue revealed ARM with positive protein S100, melanoma antigen HMB45 and melan-A expression. After the diagnosis was established, abdominoperineal resection of the anus and rectum was performed, since the tumor was large, obstructive, and the anal sphincter was invaded.

Because of the possible impact of intensive SD to the cross-link between Malassezia yeasts AhR agonists and skin carcinogenesis, we discussed on this matter and reviewed the literature data regarding ARM. In addition to “pathogenic” and “non-pathogenic” Malassezia subtypes based on AhR agonist production, future studies on Malassezia metabolites, their carcinogenic effect in the skin and development of melanoma are needed. If the cross-link between Malassezia AhR agonists and skin carcinogenesis exists, timely prevention of ARM could be done with Malassezia eradication, especially in patients with severe SD.