Characterization of innate responses elicited by neoadjuvant radio-chemotherapy for rectal cancer

Abstract

e15044 Background: The neoadjuvant chemo-radiotherapy (CT-RT) has improved the treatment of locally advanced rectal cancer reducing the local recurrence. However a survival benefit has not been reached yet. In order to increase the rate of pathological complete remissions in our Institution we intensified both the CT schedule adding oxaliplatin to 5-FU and the RT program with tomotherapy. The aim of this study was to verify: whether the pattern of innate response elicited by the neoadjuvant CT-RT is heterogeneous among pts and whether this information can be used to identify which pts will benefit from the treatment. Methods: We collected samples of T3N+M0 rectal cancer pts before, during and after neoadjuvant CT-RT (3 cycles of oxaliplatin + 5-FU; 45 Gy). At each time point we characterized circulating monocytes by flow cytometry, infiltrating macrophages by immunoistochemistry (IHC) and selected inflammatatory molecules by ELISA.Results: We recruited so far 25 pts, of whom 10 have reached the surgery with three pathological complete remission and four down staging. No substantial changes were detectable in the number of circulating monocytes. In contrast we observed a clear expansion of CD14/CD86 and CD14/CD163 double positive subsets. This event was transient and apparently causally related to the treatment since it abated at the later time point. Moreover, it correlated with sensitivity to the treatment: 5/7 pts who underwent disease regression had an early and transitory increase of the number of CD14/CD86 and CD14/CD163 positive cells, which was absent or negligible in non responder pts. The IHC study revealed a massive tumoral infiltration by macrophages which displayed clear features of alternative M2 polarization as assessed by expression of the CD163 and 206 scavenger receptors. A subset of pts had elevated PTX3 and low CRP concentration at the onset of treatment. PTX3 concentration abated after the first CT cycle. Conclusions: These data suggest that neoadjuvant CT-RT modulates the cellular components of innate immune responses, that could represent valuable predictive factors. No significant financial relationships to disclose.