Uterine adenomyosis is rarely a precursor of malignant tumors, but the most frequent histological subtype is endometrioid carcinoma. We observed a rare case of mucinous carcinoma originating from uterine adenomyosis.
A 63-year-old Japanese woman presented to our hospital with lower abdominal pain. She had no atypical genital bleeding. Ultrasound demonstrated thickening of the entire uterine wall, but the endometrium was not thick. Magnetic resonance imaging demonstrated an enlarged uterus with thickening of the entire uterine wall, suggesting adenomyosis. On the basis of the specimen of endocervical curettage, adenocarcinoma originating from the endometrium was suspected. Total abdominal hysterectomy and bilateral salpingo-oophorectomy were performed to confirm the diagnosis. Macroscopically, the resected enlarged uterus had no nodules and exudation of mucin was observed from the cut surface of the thickened myometrium. The surface of the endometrium was smooth. On histological examination, mucinous carcinoma invaded almost the entire myometrium. Adenomyotic lesions were distributed focally in the uterine wall, and transition from adenomyotic glandular epithelium to mucinous carcinoma was detected within several foci. Although adenocarcinoma cells proliferated adjacent to the endometrium, the primary endometrial epithelium was atrophic without atypia. Throughout the myometrium, the mucinous carcinoma cells proliferated and floated in dilated lymph vessels with abundant mucin pools. We diagnosed this case as mucinous carcinoma originating from adenomyosis. Although the patient received 11 courses of intravenous adjuvant chemotherapy, she died of disease 18 months after the first operation.
As only one case of mucinous carcinoma originating from adenomyosis has been reported to date, this is the second case report of mucinous carcinoma. Moreover, an abnormal manner of proliferation with marked lymphatic permeation of the tumor cells throughout the myometrium was observed.

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