Comparison of Fluorescence In Situ Hybridization (FISH) and Dual-ISH (DISH) in the Determination of HER2 Status in Breast Cancer

Abstract

The determination of HER2 amplification is critical to selecting appropriate patients for HER2 targeted therapy in breast cancer. Dual in situ hybridization (DISH), an alternative to fluorescence in situ hybridization (FISH) and immunohistochemistry, is now available. To compare the FISH and DISH methods, we tested 251 samples enriched for common or difficult-to-assess HER2 anomalies. Seven samples failed DISH testing. There was a 64% (156/244) concordance between FISH and DISH by anomaly (κ = 0.58, 95% confidence interval, 0.51-0.65; P < .0001) and an 83% (203/244) concordance by amplification status (κ = 0.58; 95% confidence interval, 0.47-0.69; P < .0001). DISH resulted in lower estimates of HER2/ centromere 17 ratios than FISH, and many cases that were equivocal with FISH were normal with DISH. DISH did not detect any case with coamplification of HER2 and centromere 17. Using a cohort of difficult specimens, we observed less than 95% concordance between FISH and DISH. DISH may underestimate the HER2/chromosome 17 ratio, or FISH may overestimate this ratio.

Comparison of fluorescence in-situ hybridisation with dual-colour in-situ hybridisation for assessment of HER2 gene amplification of breast cancer in Hong Kong

“…Agreement was less at a higher HER2/CEP17 ratio, and DISH tended to underestimate the result. This is similar to the findings by Mansfield et al 20 Cohen's Kappa coefficient in our study was 0.882. Reports by other studies vary, from >0.9 in the study by Horii et al 18 in which only 48% of cases studied were of the equivocal IHC category, to 0.58 by Mansfield et al 20 who focused on samples enriched for difficult-to-assess HER2 anomalies.…”

“…11,17,18,20 The failure rate for DISH in our case series was 3.85%, which is slightly higher than the reported failure rate of 0% to 2.8% in previous studies. 17,18,20 This may be explained by the fact that most cases in our series were of IHC 2+ category, which is the most challenging group of cases. It is worth noting that in all cases wherein FISH or DISH analysis failed, when one test failed, the other gave useful information on HER2 gene amplification status.…”

“…The number of cases in our study was relatively small compared with other published studies, 17,18,20 with only 83 consecutive cases of equivocal IHC cases within a given time period. Although it may be argued that the further 21 cases added in the IHC-positive or -negative category may constitute sampling bias, re-analysis of the data excluding these cases made no significant difference to the findings.…”

“…To date, there remain few studies published on the accuracy of DISH compared with FISH or IHC. [17][18][19][20] This study provides more information about concordance of DISH and FISH, and is the first report from Hong Kong. In our study, FISH and DISH showed no statistical difference for HER2/CEP17 ratio and HER2 counts per nucleus.…”

“…[17][18][19][20] We have previously reported the prevalence and concordance between IHC HER2 overexpression and ISH assay of breast cancers in Hong Kong. 21 Funded by the SK Yee Medical Foundation to provide HER2 FISH testing in patients receiving treatment from public hospitals, and with subsequent FDA approval to provide the alternative HER2 DISH test, we performed a validation study in our laboratory to compare the results of FISH and DISH tests in determining HER2 status in breast cancer, before offering DISH for routine testing.…”