Evaluation of the concordance of two immunohistochemical antibodies (SP218 and MXR060) in detecting PTEN protein expression in breast cancer

PTEN protein expression is an increasingly important biomarker in breast cancer, especially for predicting the efficacy of PI3K/AKT/mTOR pathway-targeted therapy. Immunohistochemistry (IHC) is a commonly used method in clinicopathology to assess PTEN protein expression; however, the concordance of different antibodies in detecting PTEN protein expression in breast cancer has not been systematically evaluated. This study aims to compare the concordance of two commonly used PTEN IHC antibodies in clinical practice in mainland China. This single-center retrospective study included 150 hormone receptor-positive (HR+)/human epidermal growth factor receptor 2-negative (HER2−) breast cancer specimens. Immunohistochemical staining was performed using SP218 antibody (Roche/Ventana) and MXR060 antibody (Maixin Biotech) on their respective automated platforms. PTEN protein expression was categorized into loss and retained. Two senior pathologists independently reviewed the slides; cases with differing opinions were adjudicated by a third pathologist. Next-generation sequencing (NGS) was performed on cases with inconsistent antibody results to analyze PTEN gene status. Cohen’s kappa statistics were used to assess concordance between antibodies and between observers. In 150 samples, the loss rates of PTEN protein in breast cancer detected by SP218 antibody and MXR060 antibody were 23.3% and 22.7%, respectively. The overall concordance rate of the two antibody detections reached 99.3% (149/150), with a positive concordance rate of 97.1% and a negative concordance rate of 100%, and a Kappa value of 0.98, indicating excellent concordance. The inter-observer concordance Kappa values for the SP218 and MXR060 antibodies were 0.93 and 0.96, respectively. After review by a third physician, only one case showed inconsistent interpretation; NGS testing showed no mutation in the PTEN gene. The MXR060 and SP218 antibodies demonstrated excellent concordance and considerable inter-observer reproducibility in PTEN IHC assays for HR+/HER2− breast cancer. This provides evidence for the interchangeability of the two antibodies in clinical practice and offers a reference for pathology laboratories in selecting PTEN antibodies.