e14108 Background: Over the past decade, immune checkpoint inhibitors (ICI) have gained increased importance in modern cancer treatment. In this study we investigate the relationship between major lab abnormalities and ICI treatment duration. Methods: 1044 patients receiving ICIs between 2010-2018 were included in this retrospective study. The following parameters were analyzed: gender, age, race, cancer type, lab abnormalities for kidneys, pancreas, liver and thyroid, and treatment duration. Lab abnormalities were grouped and used in a scoring-system (0: no lab abnormalities, 1: one abnormal parameter, and 2: two or more abnormal parameters). For statistical analysis, Likelihood Ratio Chi-Square and Mann-Whitney U tests were applied. Results: The patient cohort included 386 female and 473 male patients with a mean age of 67.8±12.5 years. Primary cancer distribution included lung cancer (n = 439), melanoma (n = 253), head and neck cancer (n = 72), renal cancer (n = 53), lymphoma (n = 33), bladder cancer (n = 42), breast cancer (n = 28), and other malignancies (n = 124). Patients received one (n = 875) or a combination (n = 169) of ICIs for a mean of 152.2±215.8 days, with highest counts for nivolumab (n = 465), pembrolizumab (n = 275), ipilimumab (n = 95), and nivolumab & ipilimumab (n = 130) and others (n = 79). Patients with higher values in the scoring-system or more lab abnormalities had significantly longer treatment duration (Score 0: 107±170, 1: 159±199, 2: 244±282 days, p < 0.001). Furthermore, patients treated with ICI combination therapy demonstrated higher scores (1.1±0.8 vs. 0.5±0.7, p < 0.001) and longer treatment durations (236±304 vs. 127±175 days, p < 0.001). Patients with scores of ≥1 in the scoring system had improved overall survival (451±475 vs. 369±526 days, p < 0.001), and patients treated with two or more ICIs lived longer (563±524 vs. 377±496 days, p = 0.003). Therapy duration was also positively correlated with survival (Spearman’s rho correlation r = 0.64, p < 0.001). Conclusions: Our current exploratory study demonstrates associations between major lab abnormalities and both treatment duration and overall survival in patients treated with immune checkpoint inhibitors.