Immunohistochemical Expression of Cyclin D1 in Phyllodes Tumors: Insights Into Tumor Progression and Prognosis

Phyllodes tumors (PTs) are rare fibroepithelial breast tumors, albeit clinically significant. This study was implemented to investigate the immunohistochemical (IHC) expression of cyclin D1 in PT subtypes and in metaplastic spindle cell carcinoma. Fifty-three resected cases of PT subtypes were analyzed. IHC analysis assessed the percentage of positive stromal tumor cells and the intensity of cyclin D1 staining. The score was classified as either negative, low, or high positive. Statistical analysis was implemented to evaluate the outcomes. Significant variations in scores were observed among various subtypes of PT, with cyclin D1 exhibiting positive nuclear expression in the stromal component of borderline and malignant tumors ( P =0.001). Malignant PTs also showed significantly different cyclin D1 expression compared with triple-negative metaplastic spindle cell carcinoma ( P =0.028). Tumor recurrence was significantly associated with high cyclin D1 expression ( P =0.013). Receiver Operating Characteristic (ROC) curve analysis demonstrated moderate discriminatory ability, with an area under the curve (AUC) of 0.701 (95% CI: 0.535-0.856, P =0.023). Univariate analysis confirmed high cyclin D1 expression as a predictor of recurrence ( P =0.035). In conclusion, cyclin D1 overexpression provides insights into tumor progression and prognosis in PTs. Notably, positive cyclin D1 expression in metastatic malignant PT could be a diagnostic challenge, if not carefully considered within clinical context. Furthermore, the significant difference in cyclin D1 expression between malignant PT and triple-negative metaplastic spindle cell carcinoma highlights its potential utility in distinguishing between them.