CD117 expression in breast phyllodes tumors correlates with adverse pathologic parameters and reduced survival.

CD117 (c-kit) is a type III receptor tyrosine kinase encoded by the KIT gene. Deregulation of expression and mutations in the gene are implicated in various tumors. Reports of CD117 expression in phyllodes tumors have been controversial. We aim to investigate the protein expression of CD117 and mutations in the KIT gene in phyllodes tumors, and correlate the findings with pathological parameters and clinical outcome. A total of 272 cases were included in this study. CD117 expression was investigated by immunohistochemistry on tissue microarray sections. Toluidine blue staining was performed to indicate mast cells. Overall, 28 (10%) cases were CD117 positive. CD117 expression was significantly associated with tumor grade (P<0.001), increased stromal hypercellularity (P=0.003), stromal atypia (P=0.01), and stromal mitotic activity (P<0.001), permeative microscopic margins (P=0.002), and presence of hemorrhage (P=0.001). Expression was also associated with poorer overall survival (P=0.003). Nineteen cases were further selected for mutation screening through the Affymetrix OncoScan platform. No mutation of the KIT gene was found. Despite a lack of mutations in the KIT gene, CD117 protein expression is associated with unfavorable pathological parameters and poorer prognosis, suggesting an underlying role in the biology of phyllodes tumors.