Cytological clues in the distinction between phyllodes tumor and fibroadenoma

Fine-needle aspiration (FNA) sensitivity in discriminating between phyllodes tumor and its benign mimicker fibroadenoma (FA) remains low. Because a preoperative categorization of phyllodes tumor is crucial for their appropriate management, the authors undertook this study in an effort to improve the outcome of FNA by identifying reliable distinguishing features.

FNA smears from 15 and 12 histologically proven cases of phyllodes tumor and FA, respectively, were reviewed. The stromal and epithelial components were qualitatively and quantitatively analyzed. A group of cytological features that may distinguish between phyllodes tumor and FA were identified. Their value and reproducibility in categorizing phyllodes tumor cases were tested.

Three major cytological features were exclusively seen in all of, or the vast majority of, the phyllodes tumor cases; fibromyxoid stromal fragments with spindle nuclei (90%), fibroblastic pavements (93%), and appreciable number of spindles cells of fibroblastic nature among dispersed cell population (100%). The identification of these features improved the pick-up rate of phyllodes tumor from 40% to 100% and had substantial (kappa = 0.56-0.73) interobserver and almost perfect (kappa = 0.83) intraobserver reproducibility. There was no significant difference in the epithelial component characteristics between phyllodes tumor and FA. The frequency and degree of atypia in the dispersed cell population correlated well to the histological grade of phyllodes tumor.

FNA has proven to be a reliable test in differentiating between phyllodes tumor and FA with high sensitivity and good reproducibility. The importance of training and continuing education is emphasized.