New Approach in the Interpretation of Complex Triple-negative Breast Cancer Immunohistochemistry Specimens Processed With VENTANA PD-L1 (SP142) Assay.

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Triple-negative breast cancer (TNBC) is challenging to treat because of its lack of specific molecular targets. The IMMUNOPEG study aimed to evaluate a novel structured method for interpreting TNBC immunohistochemistry specimens processed with VENTANA PD-L1 (SP142) assay. The study involved 10 pathologists who evaluated 50 different immunohistochemistry specimens of TNBC with programmed death ligand 1 (PD-L1) expression considered challenging and that were previously evaluated by the scientific committee, using the NAVIFY Digital Pathology platform. Initially, the overall percent agreement (OPA) was 74%, with a negative percent agreement (NPA) of 68.2% for samples classified as negative, and a positive percent agreement (PPA) of 94.5% for positive samples. After training on the method, the OPA improved significantly to 81.6%, with the NPA increasing to 80.5% and the PPA decreasing to 85.5%. The mean percentage of the tumor area occupied by PD-L1-stained immune cells decreased from 2.5% to 1.6% post-training, approaching to the scientific committee's consensus of 1.029%. The study found that the pathologists' confidence in their assessments increased significantly when using the structured method, which was found to be easy to use by 9 out of 10 pathologists. All pathologists agreed that the structured method was useful for assessing PD-L1 expression. The study suggests that this method has potential value in interpreting challenging cases of PD-L1 immunohistochemistry (IHC) in TNBC. Further refinement and a training protocol may be necessary to enhance the method's efficiency. The potential for generalizing this structured method to other IHC procedures and pathologies warrants additional research.