Bilateral cystosarcoma phyllodes of the breast: a case report of malignant form with contralateral benign form.

Bilateral cystosarcoma phyllode is uncommon; bilateral tumors, either synchronous or metachronous, are generally either benign or malignant. We report one case of bilateral synchronous cystosarcoma phyllode in a 32-year-old pregnant woman. The left breast mass, measuring 21 x 17 x 10 cm, was classified as malignant cystosarcoma phyllode (high cellularity, stromal overgrowth, marked nuclear atypia, necrosis, mitotic rate = 4 mitoses/10 high power field, infiltrative margin). The right 9 x 9 cm mass was a benign cystosarcoma phyllode tumor (low to moderate cellularity, discrete nuclear atypia, mitotic rate = 1 mitoses/10 high power field, no necrosis, pushing margin). The patient had a left-sided mastectomy and a complete local excision with clear margin of the right breast mass. The patient is free of disease with a 17-month follow-up.