Can phyllodes tumours of the breast be distinguished from fibroadenomas using fine needle aspiration cytology?

In an attempt to determine whether it is possible to distinguish phyllodes tumours (PTs) of the breast from fibroadenomas (FAs) using fine needle aspiration cytology (FNAC), we reviewed the cytological slides of eight histopathologically confirmed PTs (six benign and two malignant) and compared them with cytological features of 13 histopathologically confirmed FAs. Each author independently, "blindly" assessed architectural and cytological features of the stromal (six features) and epithelial (seven features) components and the cytological background (three features) and gave a favoured diagnosis for each case. Four of six benign PTs, one of two malignant PTs and 11 of 13 FAs were correctly diagnosed cytopathologically by at least three of the authors. The presence of hypercellular stromal fragments was the most useful feature in distinguishing PTs from FAs, and the presence of cytological atypia of the stromal cells was the most important feature in distinguishing malignant from benign PTs. Sampling error was the most common reason for cytological misdiagnosis of PTs. The two FAs misdiagnosed as PTs were each of cellular type. The results of this study suggest that it is possible to distinguish PTs from FAs using FNAC in most cases. We recommend that if hypercellular stromal fragments are identified in a FNAC specimen of a fibroepithelial lesion, the cytopathologist should raise the possibility of a PT and the surgeon treat the patient accordingly.