Abstract P2-15-02: HER2 discordant results in local vs. central testing in the phase 3 nelipepimut-S trial and implementation of Leica Bond Oracle HER2 Immunohistochemistry (IHC) System for low and intermediate levels (1+, 2+) of HER2 protein expression as a companion diagn

Abstract

Abstract Background : The distinction between HER2-positive (IHC 3+ or 2+ with FISH ratio >/= 2) and not overexpressing HER2 has been the focus of many diagnostic tests over the past years in association with development of HER2-targeted therapies. The paucity of therapies developed for the low to intermediate HER2 protein expression populations has resulted in limited attention to their diagnostic precision and accuracy. The development of NeuVaxTM (nelipepimut-S; Galena Biopharma, Inc.) in the defined population requires a HER2 IHC 1+/2+ diagnostic that precisely and accurately ensures identification of targeted patients. We describe discordance rates between local and central testing performed to identify tumors with HER2 IHC 1+/2+ expression that supports the development of a method to validate HER2 1+ and 2+ (FISH < 2.2) patients who receive nelipepimut-S adjuvant therapy. Methods : The Prevention of Recurrence in Early Stage, Node-Positive Breast Cancer with Low to Intermediate HER2 Expression with NeuVaxTM Treatment (PRESENT) study, is a multicenter, multinational, prospective, randomized, double-blind, controlled Phase 3 study assessing efficacy and safety of the peptide vaccine nelipepimut-S, in HLA A2 or A3 positive patients with early stage, node positive breast cancer expressing low and intermediate levels (IHC 1+/2+) of HER2 protein. PRESENT 2-step screening includes HLA testing and central lab confirmation of HER2 1+ or 2+ expression using the DAKO HercepTest. Results : As of 2 June 2014, 1454 patients underwent central IHC testing for HER2 and had a quantifiable result of 0, 1+, 2+, or 3+ for both local and central test. Per local testing, 61% (HER2 1+, n=612; HER2 2+, n=275) were eligible and 39% (HER2 0, n=468; HER2 3+, n=99) were ineligible. Of those eligible by local testing, 67.5% (n=599) were confirmed as eligible per central testing for a discordance rate of 32.5% (n=288). Of the 288 discordant samples tested centrally, 73.6% (n=212) and 26.4% (n=76) were reported as HER2 0 and 3+, respectively. 8.7% (76/877) of patients found to be HER2 1+ or 2+ by local testing were determined to be HER2+ (IHC3+) by central testing. Conclusions : Current tests for HER2 expression are defined by their ability to determine 3+ positivity, yet significant discordance still occurs with nearly 9% false negative rate in this trial. Similarly, marked discordance exists between local and central laboratory test results for HER2 by IHC at 1+/2+ levels of expression. The relatively high discordance rate observed may be due, in part, to the lack of a validated IHC assay for low-to-intermediate expression of HER2 (0, 1+, and 2+). In order to improve accuracy of testing and to develop a companion diagnostic for nelipepimut-S, the Leica Bond Oracle HER2 IHC System has been validated to determine samples across the IHC spectrum (0, 1+, 2+ and 3+) and is now incorporated into HER2 screening for the PRESENT trial as a companion diagnostic to increase accuracy, precision, and specificity in discerning HER2 1+ and 2+ patients. Citation Format: Michelle Melisko, Elizabeth A Mittendorf, Sufia Safina, Michael Schenker, Murray A Brunt, Maria Litwiniuk, John Mackey, Katarina Petrakova, Svitiana Alieva, Lacey Chance, Gavin S Choy, Mark Ahn, Adamm Hamm, Sonia Kumar, Hope S Rugo. HER2 discordant results in local vs. central testing in the phase 3 nelipepimut-S trial and implementation of Leica Bond Oracle HER2 Immunohistochemistry (IHC) System for low and intermediate levels (1+, 2+) of HER2 protein expression as a companion diagn [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P2-15-02.