CAP Enhances Immunohistochemical Assay Validation Guideline for Better Patient Care

The College of American Pathologists (CAP) updated the “Principles of Analytic Validation of Immunohistochemical Assays” guideline to provide increased precision and accuracy of clinical immunohistochemical assays. This update assesses evidence published since the release of the original guideline in 2014 and provides new recommendations on how to analytically validate/verify immunohistochemical assays used for diagnostic and predictive purposes.

The recent update to the guideline on analytic validation/verification of immunohistochemical assays, overseen by guideline chair Jeffrey D. Goldsmith, MD, FCAP, brings forth new and revised recommendations aimed at improving cancer treatment decision-making. Immunohistochemistry (IHC) assays play a crucial role in guiding therapeutic approaches for cancer patients, and this update focuses particularly on predictive markers while also addressing changes in validation processes for assays performed on cytology specimens.

Among the updated recommendations, laboratories are advised to achieve a minimum of 90% overall concordance between the new assay and the comparator assay or expected results during the initial analytic validation/verification for every clinically used assay. This threshold applies not only to assays for estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth receptor 2 (HER2) in breast carcinoma but also extends to all immunohistochemical markers, thus ensuring a harmonized validation standard.

Dr. Goldsmith notes that while the systematic review did not uncover significant new literature, the numerical considerations and modeling from the initial guideline remain relevant. Any unexpected results during validation/verification should prompt investigation by the immunohistochemistry medical director.

Another notable recommendation addresses predictive marker assays, such as HER2 and PD-L1, where multiple scoring systems are employed. The guideline advises separate validation/verifications based on the combination of antibody clone and scoring system.

Furthermore, specific guidance is provided for validating immunohistochemistry conducted on cytology specimens.

These updated recommendations, available in an early online release in the Archives of Pathology & Laboratory Medicine, were formulated based on an assessment of evidence published since the original guideline’s release in 2014.

For access to tools, resources, and additional information on the Principles of Analytic Validation of Immunohistochemical Assays: Guideline Update, interested parties can visit the guideline webpage on

The College of American Pathologists (CAP), as the largest organization of board-certified pathologists globally and a leading provider of laboratory accreditation and proficiency testing programs, is dedicated to promoting excellence in pathology and laboratory medicine practice worldwide, ultimately benefiting patients, pathologists, and the public alike.

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