Prognostic biomarkers in a series of stage II colon cancer.

3629 Background: Different clinico-pathological factors are used to define a group of patients with high-risk stage II colon cancer (CC) that may benefit of adjuvant treatment. Moreover, several molecular markers, such as microsatellite instability (MSI) and BRAF, have been widely investigated as prognostic factors. Recently a high stroma component (EMT+ subtypes) has also been associated with poor outcome. The aim of the study is to analyze the prognostic value of MSI, BRAF and tumor-stroma ratio in a prospective series of stage II CC patients. Methods: FFPE tissue from 432 stage II CC patients operated at Hospital Universitari de Bellvitge (1996 - 2006) were included in the study. MSI status was assessed by the analysis of 5 mononucleotide repeat markers (BAT-25, BAT-26, NR-21, NR-24 and MONO-27). BRAF V600E mutation was analyzed by single strand conformation polymorphism technique. Tumor-stroma ratio was analyzed by immunohistochemistry. Associations between molecular factors and clinical features were assessed by Chi-Squared (X2) tests. A Cox regression model was used to evaluate the Relapse Free (RFS) and the Colon Cancer specific Survival. Results: MSI status could be determined in 350 patients. 48 (14%) had MSI high (MSI-H) tumor. BRAF status could be assessed in 380 cases. 58 (15%) cases were BRAF mutated. Tumor-stroma ratio was analyzed in 407 tumor samples. 176 (43%) tumors had more than 50% intra-tumor stroma and were classified as stroma-high. MSI-H tumors were significantly located in right colon (X2 p-value = 1.03e-5), were poorly differentiated (X2 p-value = 0.003) and had more than 12 lymph nodes resected (X2 p-value = 0.037). MSI-H tumors were associated with BRAF mutation (X2 p-value = 0.02) and stroma-low (X2 p-value = 0.0005). When a molecular prognostic risk classification was performed, patients with MSI-H /stroma-low suggested a low risk of relapse comparing to MSI-H/stroma-high, microsatellite stable (MSS)/stroma-low and MSS/stroma-high patients (HR = 3.15; 95 CI, 0.76 – 13.1, p-value = 0.0602). Conclusions: MSI-H tumors have BRAF mutation as well as low intra-tumor stroma. Our results suggest that tumor-stroma ratio can explain differential prognosis in MSI-H stage II tumors.