Pleomorphic carcinoma of the breast in a 17-year-old woman.

We report a 17-year-old woman with refractory high-grade breast cancer who died early after surgery, with reference to the histogenesis of the cancer. Macroscopically, the tumor was cystic, composed of a mixture of solid and myxomatous areas. Histologically, the tumor exhibited ductal structures and areas with squamoid features. Cancer cells were markedly atypical and polymorphic, and included a mixture of bizarre and eosinophilic cells with rhabdoid feature-like free cells. Immunohistochemically, cytokeratin (CK) 8, CK 18, 34 beta E12, CD10, involucrin, CK14, and vimentin were partially positive, whereas estrogen and progesterone receptors and HER-2 were negative. These findings suggest an undifferentiated cancer whose cells have multilineage potential to differentiate into mesenchymal, basal, and squamoid cells, and it was diagnosed as pleomorphic carcinoma, which is a histological type hitherto unreported in young girls. The cancer was refractory to treatment, and the patient died 1 year and 5 months after surgery despite chemotherapy and radiotherapy.