Silver in situ hybridization compared with immunohistochemistry in assessing HER2/neu status in fine-needle aspiration cytology.

Abstract

10 Background: Fine needle aspiration (FNA) cytology is a common diagnostic tool in breast cancer used to establish diagnoses of primary, metastatic or recurrent lesions. In these settings, knowledge of the HER2/neu status is vital for optimal therapeutic decision. We examined the accuracy of HER2/neu testing in alcohol-fixed malignant aspirates. Methods: FNAs with known HER2/neu status on concurrent/subsequent surgical specimen were retrospectively identified to select a study group of malignant aspirates in cell blocks (CB) from 38 breast and 18 axillary lymph nodes. This group was enriched for HER2/neu positive cases. Sequential sections were studied by IHC using rabbit monoclonal antibody 4B5 and SISH INFORM HER2 DNA and Chromosome 17 (both by Ventana Medical Systems, Tucson AZ, USA). IHC and SISH were evaluated by two pathologists according to 2007 ASCO/CAP criteria and results were compared with HER2/neu status of paired concurrent/subsequent surgical specimen. Results: HER2/neu IHC on CB yielded 17/56 (30.6%) positive, 30/56 (53.6%) negative and 9/56 (16.1%) equivocal cases. HER2/neu SISH on CB revealed 25/56 (44.6%) amplified, 30/56 (53.6%) not amplified cases. In one case the test was uninterpretable. HER2/neu status on available on 54 surgical specimens (combined IHC and ISH results) was positive in 26 cases and negative in 28. The concordance between negative or positive IHC and SISH on cell blocks was 93.6%. SISH on cell blocks could predict the HER2/neu status in 98.2% of surgical specimens whereas after exclusion of equivocal results, IHC on cell clocks could predict it in only 91.1%. Of the 26 cases with positive HER2/neu status, IHC-CB revealed 3 cases that scored 1+ and one case that scored 0 on cell block. These cases would have been misclassified if HER2/neu was tested on CB by IHC alone. Conclusions: SISH is a reliable methodology for testing HER2/neu in alcohol fixed cytology specimens and is superior to IHC in its ability to accurately predict the final HER2/neu status. Alternatively, cases can be first tested with IHC and further tested with in situ hybridization when the score is under 3+ to avoid false negative results.