Characterization of the immune microenvironment of synchronous primary tumor and liver colorectal metastases.

3610 Background: The adaptive Th1 immune response (CD3, CD8, CD45RO T cells) observed in resected primary colorectal tumor (PCT) and liver colorectal metastases (LCM) is an important prognostic factor. Preoperative treatment modifies the LCM immune microenvironment with a significant association between pathological response and increase of T (CD3, CD8) and B cells (CD20) and downregulated T regulatory cells (FoxP3). We investigated the impact of different preoperative treatments on the quality and density of the immune infiltrates in synchronous resected PCT and LCM. Methods: Metastatic colorectal patients (n = 107) undergoing curative liver surgery for all resected LCM (n = 338) were investigated. 28 patients have been operated concomitantly for synchronous LCM (n = 102) and PCT (n = 23 available) after surgery alone (S), chemotherapy (Cht) alone, Cht + anti-VEGF and Cht + anti-EGFR. The density of CD3 (T cells), CD8 (cytotoxic), CD45RO (memory), CD20 (B cells) and FoxP3 (regulatory) in the core (CT) an...