Endometrioid carcinoma of the fallopian tube resembling a female adnexal tumor of probable wolffian origin.

Endometrioid carcinoma of the fallopian tube resembling a female adnexal tumor of probable wolffian origin (FATWO) is a rare, recently delineated, low-grade carcinoma that may be confused with both FATWO and high-grade carcinoma. Only about 20 cases have been reported so far, but it probably represents almost half of the endometrioid carcinomas of the fallopian tube. It has a better prognosis than conventional tubal endometrioid and serous carcinomas. Macroscopically, the tumors form a small, solid, polypoid mass that is usually confined within the tube. Microscopically, the tumors are characterized by proliferations of spindle cells in whorls and closely packed confluent elongated glands with focal tubular, sieve-like, and papillary structures. Unlike FATWO, this variant of endometrioid carcinoma exhibits focal squamous differentiation, intraluminal mucin, mild to moderate nuclear atypia, and occasional mitosis. Unlike FATWO, tumor cells are negative for inhibin-alpha and calretinin.