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CAP Updates Guidelines for Validation of Immunohistochemical Assays

NEW YORK – The College of American Pathologists on Friday announced that it has updated its guideline on analytic validation of immunohistochemical assays. 

The update takes into consideration evidence published since the release of the original guideline in 2014 and provides new recommendations on how to analytically validate and verify immunohistochemical assays used for diagnostic and predictive purposes, the organization said in a statement. Several new recommendations provide guidance for validation and verification of IHC assays performed on cytology specimens and predictive marker assays with distinct scoring systems, including programmed death receptor-1 (PD-L1). 

CAP now recommends that for initial analytic validation or verification of every assay used clinically, laboratories should achieve at least 90 percent overall concordance between the new assay and the comparator assay or expected results. This revision also applies to estrogen receptor, progesterone receptor, and human epidermal growth receptor 2 IHC assays performed on breast carcinoma, which previously had different concordance thresholds, CAP said. The recommendation "harmonizes validation requirements for all immunohistochemical markers," it noted.

"Although the systematic review did not identify substantive new literature, the numerical considerations and modeling discussed in the initial guideline document remains relevant," Jeffrey Goldsmith, CAP guideline chair, said in a statement. "If validation/verification yields unexpected results, the causes should be investigated by the immunohistochemistry medical director."

For predictive marker assays, such as HER2 and PD-L1, in which more than one scoring system is used, the organization recommends separate validations and verifications based on antibody clone and scoring system combination.