Immunohistochemistry validation procedures and practices: A college of American pathologists survey of 727 laboratories

Context.-The immunohistochemistry (IHC) laboratory represents a dynamic area of surgical pathology with limited practice guidelines. Studies have shown significant interlaboratory variability in results. Objective.-To establish baseline parameters for IHC validation procedures and practice, and to assess their feasibility of implementation. Design.-In September 2010, a questionnaire was distributed by the College of American Pathologists. It was composed of 32 questions relating to nonpredictive assays as well as non-US Food and Drug Administration (non-FDA)-approved, predictive IHC assays other than human epidermal growth factor 2 (HER2/neu). Results.-For non-FDA approved, nonpredictive IHC assays, 68% of laboratories had a written validation procedure. Eighty-six percent of laboratories validated the most recently introduced nonpredictive antibody. Seventy-five percent used 21 or fewer total cases for the validation and 40% used weakly or focally positive cases. Forty-six percent of respondents had awritten procedure for validation procedures for non-FDA approved, predictive marker IHC assays other than HER2/neu. Seventy-five percent of laboratories validated the most recently introduced predictive antibody other than HER2/neu. Fewer than half used 25 or more cases for the validation, and 47% used weakly or focally positive cases. Conclusion.-Some laboratories have written validation procedures that appear to build upon HER2/neu testing guidelines. Some laboratories also manage to validate new antibodies according to those standards; however, many do not. There appears to be a need for further validation guideline development for nonpredictive and non-FDA approved predictive antibody IHC assays.