Osteosarcoma arising in the breast.

We report on a 49-year-old woman with osteosarcoma arising in the breast. She had undergone two consecutive excision biopsies for right breast tumors at ages 40 and 42 years. The tumors were diagnosed as a fibroadenoma and a benign phyllodes tumor, respectively. At age 46 years, she noticed a gradually enlarging mass in the same breast. After 3 years, at age 49 years, total mastectomy was performed. The tumor occupied the entire breast and measured 12x9x8.5 cm. The tumor cells were spindle-shaped and pleomorphic, with large, irregular nuclei and distinct nucleoli. Many tumor cells had characteristics of osteoblastic and chondroblastic elements producing osteoid, osseous, and cartilaginous intracellular substances. Pathologic mitoses and apoptotic cells were frequent. Neoplastic cells had infiltrated the skin. Blood and lymph vessel invasion was present. Tumor cells expressed vimentin, osteopontin, vascular endothelial growth factor, CD10, and alkaline phosphatase, but did not express keratin. Chemotherapy was not effective. The patient died of multiple pulmonary metastases 9 months after mastectomy.