Abstract 3039: Identification of a novel biomarker of resistance to lapatinib common to both breast and oesophagogastric cancer

Abstract HER2 is amplified and/or overexpressed in 15% and 20% of breast and oesophagogastric (OG) cancers, respectively. Results from the recently published ToGA trial reveal that trastuzumab plus standard chemotherapy improves survival in patients with advanced HER2-positive OG cancer compared with chemotherapy alone, which mirrors the survival benefit shown with trastuzumab plus chemotherapy in metastatic breast cancer. The clinical value of lapatinib, already confirmed in advanced trastuzumab-resistant breast cancer, is currently being evaluated in prospective phase III trials for HER2-positive OG cancer in the metastatic setting. Despite improvements in outcome with anti-HER2 therapy, less than half of patients respond to treatment, and predictive biomarkers to lapatinib for breast and OG cancer have not yet been identified. We sought to identify predictive biomarkers of resistance to lapatinib treatment, common to both breast and OG cancer, by using a siRNA screen of genes identified in a primary siRNA screen to sensitise lapatinib-resistant breast cancer cell lines to lapatinib. These genes are found recurrently amplified and overexpressed in 45 HER2-amplified primary breast cancers and 13 HER2-amplified breast cancer cell lines. OG junction cell lines were treated with lapatinib and screened using the siRNA library. We found that silencing of TP53INP1, a gene target of TP53 which is known to be a reactive oxygen species scavenger, resulted in significant sensitisation to lapatinib in two of the most lapatinib-resistant HER2-positive cell lines derived from the OG junction. TP53INP1 was over-expressed, but not amplified, in the sensitised OG junction cell lines. Our results suggest that genes which mediate resistance to anti-HER2 therapy in breast cancer may be relevant to OG cancer. We are currently developing assays for TP53INP1 in tumours for validation within the context of prospective randomised controlled clinical trials for OG cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3039. doi:10.1158/1538-7445.AM2011-3039