Breast sarcomas with giant cells and osteoid are rare and usually fatal. They should be distinguished from carcinomas with sarcomatous metaplasia. Our case is presented together with eight similar ones reported in the English literature. Their clinical, radiologic, gross, and histologic characteristics are analyzed. Most patients died within 1 1/2 years of diagnosis, survival apparently being related to the size of the tumor. Diagnosis is delayed because the tumor can be confused clinically and radiologically with a large fibroadenoma. Awareness of this problem, fine-needle aspiration, and computerized tomography may lead to earlier diagnosis and, consequently, improved survival. In our case, immunohistochemical studies supported the notion that the lesion was a primary sarcoma, rather than a carcinoma with sarcomatous metaplasia.