The local immune phenotype influences prognosis in patients with nodal-positive rectal cancer after neoadjuvant chemoradiation.

The local immune contexture in patients with locally advanced rectal cancer (LARC) has important prognostic value after neoadjuvant chemoradiation and surgical resection. In this study, we examined the prognostic role of Indoleamine-2,3-Dioxygenase (IDO1) and infiltrating cytotoxic T lymphocytes (CD8+) according to the nodal stage of LARC patients. Expression of IDO1 and CD8 was evaluated through immunohistochemistry in 106 archival tumour tissue samples from patients following neoadjuvant chemoradiation and radical resection. The average infiltration of IDO1+ and CD8+ cells was calculated and expressed as total scores as previously described. Kaplan-Meier curves were used to describe overall and disease-free survival. In nodal-positive tumours (N+), IDO-positivity was associated with a reduced disease-free survival (DFS) (p = 0.063) and CD8-positivity with an impaired OS (p = 0.024). Patients with a N+ LARC and a high total IDO1 score showed a clear advantage regarding five-year disease-free survival rates compared with patients with a low total IDO1 score (N+ 5y-DFS IDO1 high: 66.7% vs IDO low: 19%). We also detected better 5-years-OS rates in N+ LARC with a high total CD8 score (N+ 5y-OS CD8 high: 83.3% vs CD8 low: 32.3%). These survival benefits were not evident in patients with N-tumours. Analysis of the local CD8 and IDO1 expression influences prognosis in nodal-positive LARC patients after multimodal therapy and may be a helpful tool in specifying individual adjuvant treatment strategies according to different immune profiles.