Peritoneal metastases from an atypical fibroxanthoma.

Atypical fibroxanthoma (AFX) is a mesenchymal neoplasm usually occurring in sun-exposed skin of elderly patients. The majority have an excellent prognosis, as recurrences are uncommon and metastases are rare. We present a case of an 81-year-old man who developed widespread peritoneal metastases from an AFX on his scalp, which was completely excised 3 years earlier. Histology of the scalp lesion showed a markedly pleomorphic neoplasm characteristic of AFX. Features associated with increased risk of metastasis, namely lymphovascular space invasion, deep invasion, and substantial necrosis, were not present. An extensive immunohistochemical panel was performed. The tumor cells were negative for melanocytic, epithelial, and smooth muscle immunohistochemical stains, and positive for vimentin, CD10, CD99, and focally for CD68. Histologically, the peritoneal tumor was virtually identical to the original scalp lesion and had an identical immunohistochemical profile. Electron microscopy of the peritoneal tumor revealed pleomorphic undifferentiated cells with abundant lipid vacuoles. This is the first reported case of AFX with peritoneal metastases. Although AFXs generally have an excellent outcome, pathologists must remain cognizant of the small but real potential for metastasis and this needs to be conveyed in all reports.