Uterine metastasis from a heterologous metaplastic breast carcinoma simulating a primary uterine malignancy.

OBJECTIVE: To describe the first distant metastasis of a heterologous metaplastic breast carcinoma in the uterus and discuss its differential diagnosis. METHODS: Light microscopy, immunohistochemistry, and flow cytometry were used to evaluate the tumor. RESULTS: A 58-year-old woman underwent mastectomy for metaplastic breast carcinoma confined to the breast. She presented 4 years later with vaginal bleeding. The endometrial curettage showed a poorly differentiated carcinoma. She underwent hysterectomy and bilateral salpingo-oophorectomy as well as pelvic and periaortic lymphadenectomy. Clinical and intraoperative findings favored a primary uterine malignancy. The uterus was markedly distorted with multiple gray-white, solid subserosal, and intramural tumor nodules. The tumor diffusely infiltrated the endometrium sparing benign endometrial glands. The tumor nodules were distributed full thickness of the myometrium. These nodules were composed of high-grade malignant epithelial cells with areas of chondroid metaplasia. Extrauterine microscopic tumor was present in left ovary, pelvic, and periaortic lymph nodes. The histologic features and estrogen/progesterone receptors (ER/PR) as well as DNA ploidy analysis of the uterine tumor showed striking similarity with those of the primary metaplastic breast carcinoma. A diagnosis of metastatic metaplastic breast carcinoma in the uterus was rendered. CONCLUSION: A metastatic heterologous metaplastic breast carcinoma with cartilaginous metaplasia should be considered in the differential diagnosis of heterologous uterine malignant mixed mesodermal tumor (MMMT) and high-grade endometrioid carcinoma with rare foci of cartilage.