Performance of MammaTyper in Fine Needle Aspiration Cytology, Core Needle Biopsy and Surgical Breast Cancer Samples

Objective: To evaluate the performance and concordance of the MammaTyper molecular test across cytological, biopsy and surgical samples from breast carcinomas, emphasising the applicability of cytology in molecular subtyping. Methods: 29 breast carcinoma cases, each represented by cytological, biopsy and surgical samples, were retrospectively collected from 2021 to 2025 at the Pathology Unit of Trieste. Subtyping was performed using MammaTyper on all sample types. Concordance between MammaTyper results across different sample types was assessed using Lin's concordance correlation coefficient (CCC), overall concordance rate (OCR) and kappa statistics. Results: A total of 84 samples from breast carcinoma were analysed, including FNAC, CNB and surgical resection specimens. Molecular subtyping was technically successful in all cases. When comparing IHC and MammaTyper results retrieved in CNBs, we found almost perfect agreement for ER, substantial agreement for PgR and HER2 and moderate agreement for Ki-67. Concordance rates between cytology and FFPE samples (respectively CNB and surgical specimens) showed excellent agreement for ER (CCC 0.81 and 0.835), good agreement for PgR (0.714 and 0.78), excellent agreement for HER2 (0.855 and 0.854) and moderate agreement for Ki-67 (0.626 and 0.643). In particular, discrepancies in HER2 and Ki-67 status between cytological and FFPE samples were observed in a relevant subset of cases, potentially affecting therapeutic stratification. Conclusions: MammaTyper demonstrated high concordance and reliability on cytological and biopsy samples, supporting its use in minimally invasive diagnostics. Despite the discrepancies in some markers, cytology offers a cost-effective, less invasive alternative to biopsies for molecular subtyping, aligning with precision medicine goals.