HER-2 fluorescence in situ hybridization: Results from the Survey Program of the College of American Pathologists

Context. - Fluorescence in situ hybridization (FISH) is a common method used to determine HER-2 status in breast cancer. Limited information is available concerning reproducibility of FISH in determining HER-2 gene amplification. Objective. - To present proficiency testing results of FISH for HER-2 conducted by the Cytogenetics Resource Committee of the College of American Pathologists/American College of Medical Genetics. Design. - During the past 5 years, unstained sections from 9 invasive breast carcinomas were used for HER-2 FISH proficiency testing, allowing for comparison of FISH results among a large number of laboratories. Additional data were collected using an educational (ungraded) challenge and supplemental questions in the surveys. Results. - The number of laboratories participating in HER-2 FISH proficiency testing has increased steadily during the past 5 years (from 35 in 2000 to 139 in 2004). Reproducibility of test results among laboratories was excellent for breast tumors with low copy number (no HER- 2 amplification) and for breast tumors with high copy number (HER-2 amplification). However, there was considerable variation in interpretation of results for a tumor with low-level HER-2 amplification that was tested on 2 separate occasions. Responses to supplemental questions indicated that there was a need for consensus on the use of a separate equivocal/borderline interpretative category and the need for standardization of cutoff values used to define interpretative categories. Conclusions. - The College of American Pathologists proficiency survey programs provide useful information concerning the reproducibility of clinical testing for HER-2 by FISH and reflect clinical interpretation of HER-2 FISH analyses from laboratories across the country.