CD 10 EXPRESSION IN FIBROEPITHELIAL LESIONS OF BREAST AND THEIR ASSOCIATION WITH CLINICOPATHOLOGICAL PARAMETERS

Abstract

Background: Fibroepithelial lesions (FELs) of the breast, encompassing fibroadenoma (FA) and phyllodes tumour (PT) [benign, borderline, malignant], are biphasic neoplasms representing one of the most diagnostically challenging groups in surgical pathology. Histomorphological overlap, particularly between cellular fibroadenoma and benign PT, necessitates ancillary immunohistochemical (IHC) markers. CD10, a zinc-dependent neutral metalloendopeptidase (neprilysin, MME gene), is expressed in myoepithelial cells and aberrantly upregulated in activated stromal fibroblasts, making it a candidate marker of progressive stromal transformation. The present study aimed to evaluate CD10 expression across the FEL spectrum and correlate it with established clinicopathological parameters. Materials and Methods: This cross-sectional study (prospective and retrospective) included 64 excision biopsy specimens of fibroepithelial breast lesions received between January 2018 and January 2026 at the Department of Pathology, SRM Medical College and Research Institute, Potheri. All specimens were fixed in 10% neutral buffered formalin, processed to paraffin blocks, and sectioned at 4 µm for H&E staining and IHC using the Peroxidase-Anti Peroxidase (PAP) method. CD10 IHC was performed using a monoclonal antibody (clone DBS 56C6, PATHINSITU) with microwave-based antigen retrieval. CD10 stromal expression was graded as negative/Grade 0 (<10%), weak/Grade 1 (10–30%), or strong/Grade 2 (>30%) using breast myoepithelium as an internal positive control. Statistical analysis employed the chi-square test; p < 0.05 was considered statistically significant. Results: Of 64 cases, 25 (39.5%) were fibroadenomas, 24 (37.5%) benign PTs, 7 (10.7%) borderline PTs, and 8 (12.3%) malignant PTs. CD10 expression demonstrated a highly significant stepwise increase with tumour grade (p < 0.001). Grade 2 (strong) expression was confined exclusively to malignant PT (7/8; 87.5%), Grade 1 (mild) expression predominated in borderline PT (7/7; 100%), and Grade 0 (negative) was universal in fibroadenoma (25/25) and the majority of benign PT (19/24). The diagnostic performance of Grade 2 CD10 for malignant PT: sensitivity 87.5%, specificity 100%, PPV 100%, NPV 96.4%. Conclusion:CD10 shows a progressive and statistically significant stepwise increase in stromal expression from fibroadenoma through benign to malignant phyllodes tumour, with Grade 2 (strong) expression confined exclusively to malignant PT. These findings support the integration of CD10 into multimarker IHC panels as a high-specificity adjunct marker for identifying malignant stromal transformation in diagnostically challenging fibroepithelial lesions of the breast.