HER-2/neu gene amplification in breast imprint cytology analyzed by fluorescence in situ hybridization: direct comparison with companion tissue sections.

Fluorescence in situ hybridization (FISH) is a validated method for detection of HER-2/neu gene amplification and was recently approved by the FDA for diagnostic use in paraffin-embedded tissue. Its use in cytologic specimens, however, has not been investigated. To see whether HER-2/neu gene amplification is detectable in cytologic specimens, we examined touch imprints and corresponding tissue sections of 27 breast carcinomas (20 invasive and 7 in situ) and 3 atypical epithelial hyperplastic lesions, using the FISH technique with the HER-2/neu DNA probe kit (Vysis, Inc., Downers Grove, IL). HER-2/neu gene amplification was determined, using the ratio of HER-2/neu:CEP 17 signal counts; a ratio of 2.0 or greater was considered amplified. Successful hybridization occurred in 55/60 (92%) slides. In all cases, at least one of the paired slides was adequate for evaluation. Whole-cell imprint and tissue section slides yielded comparable HER-2/neu:CEP 17 signal counts and ratios, including one case of low-level HER-2/neu gene copy numbers where the ratio was 2.0. Our findings indicate that whole-cell imprint cytology preparations are a reliable medium for HER-2/neu gene quantification by FISH, and may substitute for or complement tissue section analysis.