Abstract 3741: Adjuvant active specific immunotherapy improves survival of patients with micro-satellite stable colorectal tumors, but not with micro-satellite instable tumors

Abstract

Abstract Purpose: It has been documented that Active Specific Immunotherapy (ASI), given as adjuvant treatment, improves survival of patients with stage II and III colorectal cancer (CRC). Here we report on the effects of ASI on Micro-Satellite Stable (MSS) versus Micro-Satellite Instable (MSI) tumors. Materials and Methods: From 196 patients with stage II or stage III CRC who previously participated in the ASI trial published previously (Vermorken et al. Lancet), we collected frozen tumor samples and/or paraffin embedded tumor material. From this material DNA was extracted and microsatellite stability status was assessed. Microsatellite status was associated with clinical outcome in both the placebo and ASI treatment groups using Kaplan Meier analysis. Results: From 196 patients participating in the trial we retrieved good quality archival tumor DNA for further analysis of microsatellite stability (MS). We subsequently identified 162 (83%) MSS tumors and 34 MSI (17%) tumors. Irrespective of MS status a significant survival benefit for patients receiving ASI treatment (P=0.012) was observed, confirming previous results. New to this is that irrespective of treatment, patients with MSI tumors showed significantly less recurrences than patients with MSS tumors (P = 0.03). Taking both MS status and treatment into account we found no significant difference in survival between ASI treated versus placebo receiving patients with MSI tumors. In contrast, patients with MSS tumors benefited from ASI treatment showing a significantly improved recurrence free survival (P=<0,05). Conclusion: It can be concluded that only patients with MSS tumors will benefit from adjuvant ASI since only they showed significant improved recurrence free survival on ASI therapy. For the MSI group there is most likely no benefit of ASI therapy. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3741.