Comparison of histopathological and immunohistochemical features of fibroadenoma and low-grade phyllodes tumor

Objective: To evaluate the utility of immunohistochemical (IHC) markers—CD10, CD117, Ki-67, and p53—in differentiating fibroadenoma (FA) from low-grade phyllodes tumors (LGPTs) in breast biopsies. Methods: This cross-sectional study was conducted at Dow Diagnostic Reference and Research Laboratory (DDRRL), Karachi, from July to December 2023, following ethical approval (IRB-3052/DUHS/Approval/2023/222). A total of 94 breast biopsies (47 FA and 47 LGPTs) were included. Samples with invasive carcinoma, incomplete data, or lack of consent were excluded. Histological diagnosis was made on H&E-stained paraffin sections, followed by IHC analysis using CD10, CD117, Ki-67, and p53 markers. Expression was evaluated using an immunoreactivity score based on staining intensity and percentage of positive cells. Expression intensity was categorized into four levels: +3 (strong), +2 (moderate), +1 (weak), or 0 (no expression). Statistical analysis was performed using SPSS version-26.0. Results: Mean age was 31.7±9.2 years for FA and 35.2±10.8 years for LGPTs, with significantly larger tumor size in LGPTs (6.4±3.8 cm) than FA (3.3±1.9 cm). Morphologically, stromal hypercellularity, nuclear atypia, and leaf-like architecture were predominantly noted in LGPTs. Immunohistochemically, LGPTs showed higher moderate-to-strong expression of p53 (17 vs. 8 cases, p=0.043), Ki-67 (13 vs. 4 cases, p=0.050), CD117 (19 vs. 8 cases, p=0.024), and CD10 (8 vs. 1 case, p=0.046), compared to FA. LGPTs consistently exhibit higher proportions of moderate to strong stromal expression across all evaluated markers. Conclusion: Immunohistochemical markers CD10, CD117, Ki-67, and p53 demonstrate significant differential expression between FA and LGPTs. Their combined use can enhance diagnostic accuracy in distinguishing fibroepithelial breast lesions.