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 a written 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.