Phyllodes Tumor: A Clinicopathologic and Immunohistochemical Study of 30 Cases

Abstract

Phyllodes tumors (PTs) of the breast are biphasic neoplasms composed of epithelium and a spindle-cell stroma. Currently, PTs are classified as benign, borderline, or malignant based on histopathologic features. However, histologic classification does not always predict outcome. Objective.-To determine the prognostic value of a variety of clinicopathologic features and immunoreactivities in PTs. Sixteen benign, 8 borderline, and 6 malignant PTs with follow-up were examined for reactivity across a panel of immunohistochemical stains, including c-Kit, endothelin 1, p16, p21, p53, and Ki-67. Clinicopathologic features, including stromal cellularity, mitotic rate, and margin status, were also assessed. Tumor variables were compared among tumor subgroups and between tumors that did and did not recur. Of the 30 PTs, 4 recurred (1 benign, 2 borderline, 1 malignant). One patient with a malignant tumor died of metastatic disease 34 months after initial diagnosis. The overall positive rate of c-Kit immunoreactivity was 13% in benign, 63% in borderline, and 67% in malignant PTs. Endothelin 1 epithelial cytoplasmic staining was seen in 100% of benign, 50% of borderline, and 17% of malignant PTs. Additionally, p16, p21, p53, and Ki-67 were differentially expressed among benign, borderline, and malignant tumors. Positive surgical resection margins was the only variable that significantly predicted recurrent disease (P = .02). Stromal c-Kit positivity and epithelial endothelin 1 negativity are more often associated with malignant PTs; however, only positive margin status is significantly associated with tumor behavior.