Background: Elevated tumor-infiltrating T-cell density is associated with favorable outcomes in patients with rectal cancer treated with neoadjuvant chemoradiotherapy (CRT). Here, we evaluated the significance of programmed cell death 1 (PD-1)-positive cells, regulatory T cells, and macrophages in response to CRT and prognosis.
Patients and methods: We assessed CD8+, PD-1+, FOXP3+, CD68+, and CD163+ intratumoral and stromal cell densities by immunohistochemistry using pre-treatment biopsies from 275 patients with rectal cancer treated with neoadjuvant CRT. We determined the impact of these measurements on response to CRT and survival. Response to CRT was determined by tumor regression grade (TRG) of surgical specimens, with good responders defined as TRG3-4.
Results: Intratumoral CD8+ and PD-1+ cell densities were significantly higher in good responders than in poor responders, whereas stromal CD68+ cell density was significantly lower in good responders as compared with poor responders. The multivariable analysis revealed high intratumoral CD8+ and PD-1+ cell densities to be independently associated with good responders (CD8: odds ratio [OR], 2.27; 95% confidence interval [CI], 1.21 - 4.34, P = .010; PD-1: OR, 1.97; 95%CI, 1.03 - 3.84, P = .039), and improved recurrence-free survival (CD8: hazard ratio [HR], 0.56; 95%CI, 0.32 - 0.98, P = .044; PD-1: HR, 0.37; 95%CI, 0.19 - 0.71, P = .002). Only high intratumoral CD8+ cell density was associated with improved overall survival (P = .022).
Conclusion: Pre-treatment high intratumoral PD-1+ and CD8+ cell densities were independently associated with good response to CRT and improved recurrence-free survival, with high intratumoral CD8+ cell density additionally associated with improved overall survival. These values may serve as predictive and prognostic biomarkers in rectal cancer.
Keywords: CD8 expression; Chemoradiotherapy; Immunohistochemistry; PD-1 expression; Rectal cancer.
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