The Prognostic Role of the Host Immune Response in Rectal Cancer Patients Treated with Neoadjuvant Chemoradiation.

575 Background: The development of metachronous distant metastasis is – despite remarkable progress - still a challenging problem after multimodality treatment of rectal cancer. The host immune response has been identified as a valid prognostic marker in primary colon cancer but not in rectal cancer after neoadjuvant chemoradiotherpy so far. Methods: We analysed the mRNA and protein expression of the B- and T-cell chemokines CXCL13 and CXCL9 as well as the B-cell marker IGHM in 77 rectal cancer specimens undergoing preoperative chemoradiotherapy and investigated the role of the host immune response on the occurrence of distant metastasis and survival. Results: The intratumoral mRNA expression levels of the T-cell activator CXCL9 (p < 0.001) as well as the B-cell chemokine CXCL13 (p < 0.01) were inversely correlated with the development of distant metastasis. Patients with high CXCL9 (p < 0.0001) or CXCL13 expression (p < 0.01) had a significantly prolonged DFS. Moreover, patients with high mRNA levels of both CXCL9 and CXCL13 had an excellent DFS compared to patients without expression of any of the chemokines (p < 0.0001). Additionally, CXCL9 expression was correlated with an improved CSS (p < 0.05). There was no significant correlation between the B-cell marker IGHM and metastasis or survival. Conclusions: The host immune response represented by intratumoral expression levels of the lymphocyte-activating chemokines CXCL9 and 13 is associated with reduced rates of distant metastases and improved survival in rectal cancers after multimodality treatment. Further investigations are needed to prospectively validate these results and characterize the underlying cellular and molecular mechanisms.