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Atezolizumab in combination with nab-paclitaxel has been introduced for the treatment of locally advanced or recurrent triple negative breast cancer (TNBC). Patient selection relies on the use of immunohistochemistry using a specific monoclonal PD-L1 antibody (clone SP142) in a tightly controlled companion diagnostic test (CDx) with a defined interpretative algorithm. Currently there are no standardized recommendations for selecting the optimal tissue to be tested and there is limited data to support decision making, raising the possibility that tissue selection may bias test results. We compared PD-L1 SP142 assessment in a collection of 73 TNBC cases with matched core biopsies and excision samples. There was good correlation between PD-L1-positive core biopsy and subsequent excision, but we found considerable discrepancy between PD-L1 negative core biopsy and matched excision, with a third of cases found negative on core biopsies converting to positive upon examination of the excision tissue. In view of these findings, we developed a workflow for the clinical testing of TNBC for PD-L1 and implemented it in a central referral laboratory. We present audit data from the clinical PD-L1 testing relating to 2 years of activities, indicating that implementation of this workflow results in positivity rates in our population of TNBC similar to those of IMpassion130 clinical trial. We also developed an online atlas with a precise numerical annotation to aid pathologists in the interpretation of PD-L1 scoring in TNBC.

Alpha-methylacyl-coenzyme A-racemase (AMACR), also known as p504s, is overexpressed in prostatic adenocarcinoma and is frequently used in combination with basal cell markers to aid in diagnosing difficult prostate adenocarcinoma cases. In this retrospective method comparison study, we examined the sensitivity and specificity of the ready-to-use anti-p504s (SP116) Rabbit Monoclonal Primary Antibody compared to the monoclonal rabbit anti-human AMACR clone 13H4 in prostatic adenocarcinoma samples. De-identified prostatic adenocarcinoma tissue samples were stained with either the SP116 or 13H4 antibody clone in combination with the VENTANA Basal Cell Cocktail (34βE12+p63) and scored as positive or negative for prostatic adenocarcinoma. The scoring pathologist was blinded to the known historical diagnosis of each sample. The scoring pathologist correctly diagnosed each sample regardless of which p504s clone was used. Both assays using either clone were 100% concordant in their sensitivity and specificity. This study demonstrates that the ready-to-use anti-p504s (SP116) Rabbit Monoclonal Primary Antibody is equivalent to clone 13H4 concentrate when used according to package insert instructions in combination with the VENTANA Basal Cell Cocktail (34βE12+p63) to aid pathologists in the diagnosis of prostatic adenocarcinoma.