CAP Updates Validation of Immunohistochemical Assays Testing Guideline for Precise Results, Improved Patient Care
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NORTHFIELD, Ill. ~ NORTHFIELD, Ill.-- The College of American Pathologists (CAP) has recently released an updated version of their "Principles of Analytic Validation of Immunohistochemical Assays" guideline. This update aims to improve the precision and accuracy of clinical immunohistochemical assays by assessing new evidence published since the original guideline was released in 2014.

According to Jeffrey D. Goldsmith, MD, FCAP, chair of the guideline, this update is crucial as immunohistochemical assays often play a significant role in guiding therapeutic decisions for cancer treatment. The revised guideline provides new and revised recommendations for the analytic validation and verification of these assays, with a particular focus on predictive markers.

While many of the original statements from the 2014 guideline remain similar, there are several new recommendations that provide guidance for validating immunohistochemical assays performed on cytology specimens and predictive marker assays with distinct scoring systems. For initial analytic validation or verification of any assay used clinically, laboratories should aim for at least 90% overall concordance between the new assay and the comparator assay or expected results.

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This updated guideline also applies to estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth receptor 2 (HER2) IHC performed on breast carcinoma. These markers should also be validated at a minimum concordance rate of 90%, replacing the previously different thresholds. This recommendation aims to harmonize validation requirements for all immunohistochemical markers.

Dr. Goldsmith emphasizes that although there were no significant new findings in the systematic review conducted for this update, the numerical considerations and modeling discussed in the original document are still relevant. If unexpected results are obtained during validation or verification, it is recommended that laboratories investigate the causes with their immunohistochemistry medical director.

The updated guideline also includes a strong recommendation for predictive marker assays such as HER2 and programmed death receptor-1 (PD-L1), where more than one scoring system is used. In these cases, separate validation or verification should be performed based on the antibody clone and scoring system combination.

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Specific guidance for validating immunohistochemistry performed on cytology specimens is also provided in the updated guideline. These recommendations are now available in an early online release in the Archives of Pathology & Laboratory Medicine and were established through the assessment of evidence published since the original guideline was released.

The CAP has made tools, resources, and information for this updated guideline available on their website, This will help laboratories adhere to the "Principles of Analytic Validation of Immunohistochemical Assays" and ensure increased precision and accuracy of clinical immunohistochemical assays.
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