The concordance between NCCTG's and NSABP's C-myc FISH assays

Abstract

22110 Background: Preliminary results from the National Surgical Adjuvant Breast and Bowel (NSABP) adjuvant trastuzumab breast cancer (BC) trial, B-31, suggested that HER2-positive BC patients with primary tumor C-myc (MYC) amplification derived more benefit from trastuzumab than those patients without MYC amplification. The purpose of this pilot study was to establish the concordance between NSABP's and North Central Cancer Treatment Group's (NCCTG) fluorescence in situ hybridization (FISH) assays so that a MYC biomarker validation study can be performed. Methods: Whole sections (WS) of 85 independent HER2-positive (IHC 3+ or FISH amplified) breast tumors and sections from tissue microarrays (TMAs) containing three cores from each of these tumors were sent to NCCTG's research base (Mayo Clinic Rochester, MN) and NSABP's research base (University of Pittsburg, PA) and analyzed with probes from Abbott Molecular (Des Plaines, IL). NSABP's assay uses a single probe for the MYC gene, and a gene copy number score was provided for each WS and TMA spot. NCCTG's assay uses probes for both MYC and centromere 8 (CEP 8), and the MYC:CEP8 ratio, a calculated gene copy number score, and overall interpretation were provided for each WS and TMA spot. Results: The concordance between WS and maximum TMA score was 94% and 90% for NSABP and NCCTG, respectively; and between WS and maximum TMA MYC:CEP8 ratio was 96% for NCCTG. The WS concordance between NSABP's gene copy number score and NCCTG's MYC:CEP8 ratio, calculated gene copy number score, and overall interpretation were 80%, 93%, and 76%, respectively. Conclusions: We obtained acceptable assay concordance, which allows for cross-validation and even potential pooled analyses of NCCTG's and NSABP's MYC FISH data. These types of assay validation and concordance studies are vital to the ability to properly conduct correlative translational studies, which will be reported independently in the context of N9831, a similar adjuvant trastuzumab trial to B31. No significant financial relationships to disclose.