[250] Dual Color Chromogenic In Situ Hybridisation Seems To Detect a Different Subgroup of HER2/Neu Amplified Immunoscore 2+ Breast Carcinomas Compared to FISH

SF Lax, S Urdl, K Prein. General Hospital Graz West, Graz, Austria

Background: Fluorescence in situ hybridization (FISH) is considered the gold standard for the assessment of Her2/neu amplification. In most countries FISH is used to determine amplified breast carcinomas in the group with mild Her2/neu overexpression (immunoscore 2+). The aim of this study was to investigate whether a recently developed chromogenic in situ hybridization (CISH) technique is comparable to a well-established FISH method.
Design: 106 cases of invasive ductal carcinomas of the breast with established Her2/neu status by HercepTest Dako and Vysis FISH were retrospectively analyzed using DAKO DuoCISH. Hercep Test revealed score 2+ for 82 cases, 3+ for 16 cases and 1+ for 6 cases. Formalin fixed, paraffin embedded tissue both from core needle biopsy and from surgical specimens was used (fixation time 16- 48 hours). The Dako DuoCISH uses both a centromere probe for chromosome 17 and a probe for the Her2 gene, which are in a second step coupled with 2 different chromogens. The reaction was carried out on an autostainer according to the manufacturer's instruction. The analysis was performed according to the CAP guidelines by a single investigator using a 100x objective. All discrepant cases were reassessed.
Results: Two score 2+ cases were excluded due to a lack of sufficient tumor tissue. FISH and CISH did not differ significantly with respect to their Her2/CEP17 coefficient (p=0.9, paired t test). All score 3+ and 1+ cases were concordant in CISH and FISH (100% amplified and 100% not amplified, respectively). 24 (29%) of the score 2+ cases were amplified by FISH compared to 28 (34%) by CISH, which was not statistically significant (p=0.45; chi2 test). Comparing case by case, 12 score 2+ cases (14.6%) were discrepant between FISH and CISH with respect to amplification. 4 cases were FISH amplified/CISH non-amplified, 8 cases CISH amplified/FISH non-amplified. The Her2/CEP17 coefficient of the discrepant cases ranged between 1.2 and 4.75. Of the CISH amplified/FISH non-amplified cases, 7 had a coefficient between 2.09 and 2.75 and 2 showed a heterogeneous amplification.
Conclusions: DAKO DuoCISH seems to be a reliable technique for the assessment of Her2 amplification and allows long-term storage of the slides. The use of light microscopy enables the detection of amplified foci in heterogeneous tumors. However, DAKO DuoCISH seems to detect different Her2-amplified breast carcinomas in the score 2+ subgroup compared to Vysis FISH. Their therapeutic response as well as their outcome will have to be determined.
Category: Breast

Tuesday, March 23, 2010 1:00 PM

Poster Session IV # 16, Tuesday Afternoon


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