[674] HER2/Neu Testing in 207 Gastric and Gastroesophageal Junction Adenocarcinomas: Immunohistochemistry and Silver In Situ Hybridization (SISH) Provide Effective Brightfield Methods for Clinical HER2 Testing

Eugene Hsieh, Pauline Henry, Kevin Kwok, Wedad Hanna. Sunnybrook Health Sciences Centre, Toronto, Canada

Background: Advanced gastric and gastroesophageal (GEJ) adenocarcinomas have been shown to overexpress the HER2 receptor in a subset of cases, approximately 10-22%. ToGA, a phase III prospective randomized and multicentre trial, has demonstrated increased overall survival with anti-HER2 therapy, in patients with gastric/GEJ tumours overexpressing the HER2 receptor. Since then, status of the HER2 receptor has become an important biomarker for clinical management of these patients.
Design: Paraffin blocks from 187 primary and secondary gastric/GEJ adenocarcinoma biopsy specimens from 1999-2011 were retrieved from the archives of Sunnybrook Health Sciences Centre (SHSC), and were tested for HER2 expression using both immunohistochemistry (IHC) (Ventana PATHWAY anti-HER-2/neu 4B5), and silver in situ hybridization (SISH) (Ventana INFORM HER2 and chromosome 17 DNA probe kits). In addition, 20 consecutive outside referral biopsy specimens from 2011 were also tested, as above. IHC was scored from 0-3+ using published gastric cancer IHC interpretation criteria, with 0-1+ negative, 2+ equivocal, and 3+ positive. SISH positive (SISH+) was defined as HER2/chr.17 ratio ≥ 2.0.
Results: 28/187 (15.0%) SHSC cases were SISH+. Of these, 19/28 (67.9%) were IHC 3+ (positive) and 7/28 (25%) were IHC 2+ (equivocal). 2/28 (7.1%) were IHC 1+ (negative). No SISH+ cases were IHC 0. (p < 0.0001). For the outside referral cases, 3/20 (15.0%) had SISH overexpression, with all three cases IHC 3+. Overall 29/31 SISH+ cases demonstrated IHC 2+ or 3+ expression, with only 2/31 SISH+ cases demonstrating IHC 1+ expression. All SISH+ cases were of intestinal or mixed type. No pure diffuse type cancers had IHC 3+ expression, and all were uniformly SISH negative.
Conclusions: Since the approval of anti-HER2 therapy for gastric and GEJ cancer, HER2 testing has become necessary for patient management decisions. Traditional testing protocols have used IHC with secondary fluorescence based in situ hybridization testing when necessary. This study demonstrates excellent concordance of SISH+ and SISH- status with IHC 3+ and IHC 0 respectively, and very good concordance of SISH- status with IHC 1+. Thus, in the clinical setting, IHC can be used primarily, with reflex SISH testing of equivocal IHC 2+ cases and possibly IHC 1+ cases. This combination of IHC plus SISH provides an excellent brightfield-only alternative, allowing adoption in a greater number of pathology laboratories than is possible with fluorescence based techniques.
Category: Gastrointestinal

Monday, March 19, 2012 1:00 PM

Poster Session II # 95, Monday Afternoon


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