HER-2 in high risk rectal cancer patients treated in EXPERT-C, a randomized phase II trial of neoadjuvant capecitabine and oxaliplatin (CAPOX) and chemoradiotherapy (CRT) with or without cetuximab.

Abstract

420 Background: HER-2 is a well established therapeutic target in breast and gastric cancer. The role of HER-2 in rectal cancer is unclear, as conflicting data on prevalence of HER-2 expression in this disease have been reported. This analysis evaluates the prevalence of HER-2 and its impact on the outcome of high risk rectal cancer patients treated with neoadjuvant CAPOX and CRT ± cetuximab in the EXPERT-C trial. Methods: Eligible patients with available tumour tissue for HER-2 analysis were included. HER-2 expression was determined by immunohistochemistry (IHC) in biopsy and/or surgical specimens (score 0 to 3+). Tumours with equivocal IHC result (2+) were tested for HER-2 amplification by B-DISH. Tumours with IHC 3+ or B-DISH ratio ≥2.0 were classified as HER-2 positive. The impact of HER-2 on primary (CR) and secondary endpoints (RR, PFS, OS) of the study was analyzed. Results: Of 164 eligible study patients, 104 (63%) biopsy and 114 (69%) surgical specimens were available for analysis. Only 3/104 (2.9%) and 3/114 (2.6%) were HER-2 positive, respectively. In 77 patients with paired specimens, concordance for HER-2 status was found in 74 (96%), with 3 patients with discordant results (1 patient with HER-2 negative biopsy/positive surgical specimen, 2 patients with HER-2 positive biopsy/negative surgical specimen). Overall 141 patients were assessable for HER-2; 6/141 (4.3%) had a HER-2 positive tumour in at least 1 specimen. The median follow-up was 58.7 months. HER-2 expression or amplification was not associated with a difference in outcome for any of the study endpoints, including in the subset of 90 KRAS/BRAF wild type patients treated ± cetuximab. Conclusions: Based on the low prevalence of expression as recorded in the EXPERT-C trial, HER-2 does not appear to represent a useful therapeutic target for high-risk rectal cancer. However, the role of HER-2 as prognostic factor and potential predictive biomarker for cetuximab-based treatment in rectal cancer warrants further investigation. A more comprehensive B-DISH analysis in IHC 0/1+ tumours is currently ongoing and data will be presented at the meeting.