The impact of pre-analytical parameters on class II biomarkers by immunohistochemistry: concordance across four tissue processing protocols.

In the modern era of precision medicine, a number of class II immunohistochemistry (IHC) biomarkers are routinely tested in pathologic laboratories to select cancer patients who may be candidates for hormonal, targeted, and immune therapies. Pre-analytical factors, including tissue processing, are critical components of biomarker testing and require validation to ensure reliable results. In this study, we aimed to study the impact of tissue processing on biomarkers (including ER, PR, HER2, mismatch repair (MMR) proteins, BRAF V600E, and PD-L1) in a large prospective cohort of 109 tumors. We found that ER and MMR were not impacted; PR, HER2, and BRAF V600E were minimally affected; and PD-L1 regardless of the antibody clone was strongly influenced by a combination of tissue processing procedures and intratumoral heterogeneity. Our findings suggest that validation of pre-analytical parameters, such as tissue processing, is important for certain class II biomarkers, in particular PD-L1 IHC.