e14156 Background: Checkpoint inhibitors in cancer therapy have shown survival benefits in the treatment of several ATs. However, the risk of serious side effects seems greater in certain types of tumors presenting reduced compliance with therapy. The aim of this study is to evaluate the safety profile and clinical benefits of IT, as appraised using clinically related biomarkers of pts outside clinical trials. Methods: In this retrospective study, data were evaluated on pts in the Reggio Emilia Provincial Oncology Network who were treated for ATs using Nivolumab, Pembrolizumab and Ipilimumab monotherapy in clinical practice. The pts included in the study had received at least 1 dose of IT by June 2018. LDH and neutrophil–lymphocyte ratio (NLR) were collected at baseline, antibiotic therapy (ATB) was considered during IT, and immunorelated adverse events (irAEs) were assessed with CTCAE v.4.1. Results: A total of 169 pts were examined: 78 with NSCLC, 57 with melanoma, 29 with kidney cancer, 3 with head-neck cancer and 2 with colorectal cancer. 123 pts (73%) were treated with Nivolumab, 36 (21%) with Pembrolizumab and 10 (6%) with Ipilimumab. Overall, 62 pts (37%) experienced irAES of any degree: 17/29 (59%) pts with kidney cancer presented irAES, while only 35% (20/57) and 31% (24/78) of pts with melanoma and lung cancer did, respectively. A total of 27/62 (43%) pts delayed IT due to toxicity, but only 7/62 (11%) pts discontinued treatment due to irAEs. Statistically significant increases in PFS (11 vs. 5 months, p = 0.002) and OS (19.9 vs. 8.7 months, p = 0.002) were found between pts who experienced irAEs and those who did not. As previously demonstrated in other groups of pts, in the Cox regression performed for OS, a baseline value of LDH≥1.5xULN and median NLR ≥2.93 correlates with poor prognosis. Unlike what is already known, the use of ATB during IT (35% of pts) correlates with increased survival (HR 0.59; IC95% 0.37-0.94, p = 0.028). Conclusions: These data confirm the tolerability of IT in an unselected real-world population. In particular, the development of irAEs could be considered a positive predictor of outcome, but with a different incidence among MTS.