[762] Concordance and Interobserver Agreement of HercepTest™ and 4B5 Immunohistochemical Staining in Gastric Carcinoma

M L Wallander, M E Salama, S L Perkins, L J Layfield. ARUP Institute for Clinical & Experimental Pathology, Salt Lake CIty; Univeristy of Utah, Salt Lake City

Background: Reliable and reproducible detection of HER2 overexpression in gastric carcinoma is essential for determining patient eligibility for trastuzumab (Herceptin™) therapy. HercepTest™ and 4B5 immunohistochemistry (IHC) were directly compared to determine the performance characteristics of each assay for detection of HER2 status in gastric carcinoma.
Design: Twenty-six formalin-fixed, paraffin-embedded gastric adenocarcinomas were evaluated for HER2 status by IHC (HercepTest™ and 4B5) and fluorescence in situ hybridization (FISH) (PathVysion®). IHC slides were reviewed by two pathologists. Interobserver agreement and methodology concordance were determined for HercepTest and 4B5, using FISH as the gold standard.
Results: Agreement between HercepTest and 4B5 results was 81% (21/26). There was a noticeable tendency for higher scoring with 4B5 as compared to HercepTest™.

Table

	HercepTest 0	HercepTest 1+	HercepTest 2+	HercepTest 3+
4B5 0	7	0	0	0
4B5 1+	6	1	0	0
4B5 2+	2	3	2	0
4B5 3+	1	1	1	2

Interobserver agreement among 2 IHC viewers for HercepTest™ or 4B5 was 77% (20/26) and 73% (19/26), respectively. All 4B5 discrepant cases were correctly classified, as confirmed by FISH, for clinical decision. Correct clinical classification was achieved in 5 of 6 discrepant HercepTest™ cases. Concordance with HER2 FISH was 89% (23/26) for HercepTest™ and 96% (25/26) for 4B5.
Conclusions: Evaluation of HER2 overexpression in gastric carcinoma by 4B5 shows higher concordance with HER2 FISH compared to HercepTest™. There was no significant difference in interobserver variability between 4B5 and HercepTest™.
Category: Gastrointestinal

Tuesday, March 20, 2012 1:00 PM

Poster Session IV # 53, Tuesday Afternoon