Pseudomyxoma cutis; a new entity.

Pseudomyxoma (PM) implies an accumulation of a large amount of mucins which show myxomatous appearances. PM Peritonei (PMP) is famous and the only example of PM. PMP means excessive accumulation of mucins and mucin-secreting cells in the peritoneal cavity. The causes of PMP are mostly mucinous tumors, both benign and malignant, of ovaries and vermiform appendix. The author experienced excessive accumulation of mucins and mucin-producing cells in the subcutis and deep soft tissue. This situation very resembled PMP. Thus, the author termed the lesion as PM cutis (PMC). A 57-year-old man admitted to our hospital because of multiple subcutaneous large tumors in the perianal skin. The tumors were deeply seated and soft. No biopsy was performed. Very large skin and subcutis resection of the perianal region was done. Grossly, the material was skin and sot tissue flap measuring 25x25x5cm. The subcutis and deep soft tissue were resected. On cut surface, the tumor was slimy liquid. Microscopical examination revealed a large amount of mucins pools and mucin-producing intestinal epithelium with mild atypia. The author diagnosed it metastatic extremely well differentiated adenocarcinoma producing mucins, and pointed out anorectal primary. Thus, Miles operation was performed, which showed tumor formation in the anus. The tumor was located from the submucosa to adventitia, and composed of mucin pools and mucins producing intestinal-type epithelium with atypia. Mucins histochemistry showed that the mucin pools and epithelial cytoplasm contained neutral, carboxylated, and sulfated mucins. Immunohistochemically, the tumor cells were positive for CKAE1/3, CKCAM5.2, CK7, CK8, CK19, CK20, CEA, CA19-9,CD68, MET, p53, MUC2, MUC5AC, KIT, PDGFRA, chromogranin, and Ki-67 (76%). They were negative for CK34BE12, CK5/6, CK14, CK18, EMA, vimentin, desmin, smooth muscle actin, p63, CD34, ER, PgR, CA125, MUC1, MUC6, CD45, CD10, synaptophysin, surfactant Apo-A, TTF-1, NCAM, bcl-2, CDX-2. Although the atypia is mild, the author diagnosed primary anorectal extremely well differentiated adenocarcinoma with excessive production of mucins. The author considers the cutaneous mucins and tumor cells are metastatic or directly invading lesions of the anal tumor. Thus, the author termed pseudomyxoma cutis (PMC) for the cutaneous lesion.