Clear cell adenocarcinoma arising from adenomyosis.

A 73-year-old postmenopausal Japanese woman presented with a complaint of slight fever and weight loss. An elevated level of CA125 in the blood favored a diagnosis of malignant uterine body tumor, but was not confirmed by endometrial cytology and biopsy. Resection of the uterus revealed a solid whitish tumor in the myometrium that was diagnosed as clear cell adenocarcinoma (CCA) arising from adenomyosis. There were transitions between endometrial epithelium of adenomyosis, noninvasive CCA, and invasive CCA. Immunohistochemical expression of hepatocyte nuclear factor-1beta supported the diagnosis of CCA. Only one other English language document pertaining to CCA arising from adenomyosis exists. Malignant tumor arising from adenomyosis should be considered as a differential diagnosis when the serum level of tumor markers such as CA125 is high and when the tumor is intramyometrial.