Correlation of Cytology and Histology of Breast Phyllodes Tumor: Atypical Spindle Cells and Multinucleated Cells

A case of clinically malignant phyllodes tumor (PT) of the breast is reported. A 55-year-old woman with a lump in her left breast, which had been diagnosed as a fibroadenoma by fine needle aspiration (FNA) cytology five year before, noticed abruptly accelerated growth of the tumor. Repeated FNA cytology revealed atypical spindle and multinucleated cells, but the origin of these atypical cells could not be specifically determined. The rapid growth of the tumor resulted in an open skin ulcer and an emergent mastectomy was performed to control the intractable bleeding from the ulcer. The histological diagnosis was PT. The cytological and histological findings were compared, and there was favorable correlation. Although the tumour was clearly malignant clinically, it did not fulfill the WHO criteria for malignant PT completely. The desirable modification of the diagnostic criteria for malignant PT is discussed.