Scientific and Regulatory Policy Committee Points to Consider*: Sample Selection, Assay Design, Data Generation and Interpretation, and Reporting Practices for Chromogenic Immunohistochemical (IHC) Assays in Nonclinical Drug Development

Chromogenic immunohistochemistry (IHC) is an important molecular localization assay in biomedical research and nonclinical drug development, enabling the visualization of specific epitopes within tissues. The methodology is widely used in drug target selection, risk assessment, understanding disease biology, and characterizing histopathological findings in nonclinical studies. The Scientific and Regulatory Policy Committee of the Society of Toxicologic Pathology formed a working group to compile essential information on chromogenic IHC assays not performed in compliance with Good Laboratory Practice (GLP) from nonclinical studies, using relevant literature and the Working Group members' collective expertise. In this "Points to Consider" article, emphasis is placed on factors influencing IHC data quality, including sample selection, general assay considerations, data generation and interpretation, and effective reporting. The Working Group members deliberated extensively on pertinent topics, aiming to provide specific and practical guidance for pathologists, histologists, and allied scientists engaged in chromogenic IHC assays. While refraining from an exhaustive exploration of the intricate technical details associated with chromogenic IHC, this article offers insights to enhance the accuracy, credibility, and reproducibility of chromogenic IHC, thereby facilitating informed decision-making in the nonclinical development of biomedical products.