Role of MSI and DCC status to predict response to FOLFOX in metastatic colorectal cancer

Abstract

21056 Background: Microsatellite instability (MSI) and lack of Deleted Colon Cancer (DCC) protein expression have been observed respectively in ∼15% and 70% of colon cancer cases and are considered as prognostic factors in colorectal cancer (CRC). In adjuvant setting these markers could be considered to decide treatment. We know that MSI colon cancer do not benefit from 5Fluorouracyl (5FU)-based chemotherapy. A current treatment of reference for colon cancer is a combination of 5FU and Oxaliplatin (FOLFOX). Our aim was to determine whether MSI status or DCC expression are predictive markers of FOLFOX efficiency in patients with metastatic CRC. Methods: Tumour specimens were collected from patients with metastatic colon cancer treated with FOLFOX. The FOLFOX regimen was evaluated in first line treatment according to the WHO criteria. The microsatellite instability status was assessed by measurement of the length of five monomorphic mononucleotide markers. DCC protein expression were evaluated by immunohistochemistry. Results: Forty patients (22 men, 18 women), median age 63.5 years (27–83) were treated with FOLFOX. Nine patients had tumours exhibiting high microsatellite instability (microsatellite instability group, MSI group) and 31 patients had tumours exhibiting microsatellite stability (microsatellite stable group, MSS group). In MSS group, we observed 11 partial responses (36%) and only two in MSI group (22%) (not significant difference). Both disease free survival and overall survival were not significantly different for MSI and MSS groups. Determination of DCC status is under investigation. Conclusions: There was no significant difference in chemosensitivity to FOLFOX for MSI and MSS metastatic patients. Therefore FOLFOX regimen could be proposed to metastatic patients irrespective of MSI status. The study of the relationship between DCC expression and response to FOLFOX is ongoing. No significant financial relationships to disclose.