Association of IMP3 and CD10 Expression with Clinicopathological Features and Outcomes in Phyllodes Tumors: A Retrospective Single-Center Study

<b>Background/Objectives:</b> Phyllodes tumors (PTs) are rare fibroepithelial breast neoplasms with highly variable clinical behavior. Identifying predictive immunohistochemical markers is crucial for early detection of lesions with malignant potential and appropriate treatment selection. This study aimed to evaluate the association of insulin-like growth factor II mRNA-binding protein 3 (IMP3) and cluster of differentiation 10 (CD10) expression with histopathological grade and survival outcomes in PTs. <b>Methods:</b> We retrospectively analyzed sixty-eight female patients with PTs at Uludag University Faculty of Medicine Hospital, between 2000 and 2024. Histopathological features, IMP3 and CD10 expression, and clinical outcomes were evaluated. Disease-free survival (DFS) and overall survival (OS) were estimated using the Kaplan-Meier method and compared using the log-rank test. <b>Results:</b> Among the 68 patients (median age: 39.0 years), 60.3% had benign PTs, 14.7% had borderline PTs, and 25.0% had malignant PTs. Histopathological parameters differed significantly across grades (all <i>p</i> < 0.01). IMP3 expression was strongly associated with higher histological grade, larger tumor size, and stromal atypia (<i>p</i> < 0.05). OS differed significantly by histological grade (<i>p</i> = 0.009) and IMP3 status (<i>p</i> = 0.013), whereas DFS and CD10 expression showed no significant associations (<i>p</i> > 0.05). <b>Conclusions:</b> IMP3 expression is strongly associated with malignant histology and poorer overall survival in PTs; however, its independent prognostic value could not be conclusively established due to the limited number of outcome events. While IMP3 may serve as a promising marker in routine pathological assessment, validation in larger, prospective cohorts with sufficient event numbers is warranted.