Background: radiotherapy is a standard of care for locally advanced stage III (N2) non-small cell lung cancer (NSCLC) combined with surgery and/or chemotherapy. Radiotherapy is hypothesized to induce intra-tumoral immune infiltration via neoantigen release from dying tumor cells sometimes resulting in an abscopal effect. However, intra-tumoral immune cell characteristics that predict radiotherapy efficacy have not been identified.

Patients and Methods: we retrospectively analyzed tumor samples and clinical data from 113 patients, 89 resected) and 24 non-resected stage III (N2) NSCLC treated within the same radiotherapy department (2002 to 2015). We performed multiplex staining (CD8, FoxP3, PD-L1, pan-keratin) in order to correlate immune environment (density and location) to overall survival (OS) and disease free survival (DFS).

Results: high density of CD8+ T cells was associated with DFS (p=0.0036, HR=2.42 [1.31 - 4.47]) and OS (p=0.049, HR=1.93 [0.99 - 3.78]) in resected group only. High density of CD8+/FoxP3+ double positive T cells was associated with OS (p=0.017, HR= 1.97 [1.11 - 3.48]) in the global population; and in resected group for OS (p=0.05, HR=1.92 [0.98 - 3.74]) and PFS (p=0.03, HR=1.83 [1.03 - 3.23]), with a trend of significance for OS and PFS in the non-resected group (p=0.06, HR=2.84 [0.88 - 9.13] and p=0.05, HR=3.03 [0.91 - 10.10], respectively). Intermediate PD-L1 expression in tumor cells (TPS=1-49%) was associated with a higher survival in the resected group.

Conclusions: we demonstrated that intra-tumoral CD8+ T cell and particularly the CD8+/FoxP3+ cell density predict radiotherapy efficacy and survival in stage III N2 NSCLC. Thus, it suggests that radiotherapy rather improves than promotes tumor immunogenicity.

Citation Format: Yoan Velut, Geoffroy Boulle, Audrey Mansuet Lupo, Laure Gibault, Hélène Blons, Jean Tredaniel, Ludovic Fournel, Aurélie Boni, Isabelle Cremer, Marie Wislez, Veronique Duchatelle, Scott Hammond, Marco Alifano, Philippe Giraud, Diane Damotte. Radio-chemotherapy efficacy is predicted by intra-tumor CD8+FoxP3+ double positive T cell density in locally advanced non-small cell lung carcinoma [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4304.