INTRODUCTION: KRAS mutation the most common molecular alteration in advanced non-small cell lung cancer (NSCLC) and is associated with an unfavourable prognosis, largely due to the lack of targeted therapeutic options for the majority of the KRAS mutated isoforms. The landscape of NSCLC treatment has expanded with the introduction of immune checkpoint inhibitors (ICIs). Nonetheless, data regarding the efficacy of ICI in NSCLC patients harbouring KRAS mutations are conflicting. This study aimed to compare clinical outcomes of ICIs in advanced NSCLC with different isoforms of KRAS mutations. METHODS: A retrospective study was conducted on 143 patients with advanced NSCLC harbouring different KRAS mutation and treated with immune checkpoint inhibitors (ICI) between December 2020 and July 2022 at "Fondazione IRCCS Istituto Nazionale dei Tumori" in Milan. Log-rank and Cox Hazard methods were used for survival analysis. RESULTS: We evaluated 143 patients with advanced non-small cell lung cancer (NSCLC) harboring KRAS mutations. The most common mutation was G12C (41 %), followed by G12V (23.7 %) and G12D (11.8 %). The G12C mutation was notably associated with a higher incidence of bone metastases (42 %). Immunotherapy was administered as monotherapy in 54.5 % of cases, while 69 % received it as part of a first-line combination with chemotherapy. Co-mutations were detected in 52 % of patients, with Q61 (63 %) and G12C (58 %) being the most prevalent. Among these, 24 % had STK11 co-mutations, and 29 % had TP53 co-mutations. No significant differences in overall survival (OS) or progression-free survival (PFS) were observed across different KRAS subtypes. The longest OS was seen in patients with Q61 (46.5 months), 13X (31.8 months), and G12C (28.7 months). The highest overall response rate (ORR) of 73 % was observed in the G12D group, particularly with the combination of chemoimmunotherapy, where stable disease was the most common outcome at 40 %. The median duration of response (DOR) was 7.4 months across both treatments. The longest DOR was seen in the G12V group at 10.2 months, with no significant difference between treatments. In contrast, the shortest DOR was in the G12A group, with 1.54 months in those treated with combination therapy compared to 2.57 months with single-agent therapy. Regarding co-mutations, patients with STK11 co-mutations had a higher median OS than those without (39.7 vs. 26.1 months), but this was not statistically significant (p = 1). Similarly, TP53 co-mutations were associated with a lower median OS (19.1 vs. 26.1 months, p = 0.7), though this too was not statistically significant. Importantly, bone metastases emerged as a significant adverse prognostic factor, nearly doubling the risk of mortality (HR: 2.81, p < 0.001), regardless of KRAS subtype or co-mutation status. CONCLUSION: KRAS mutation subtypes demonstrate varying clinical outcomes. Although no statistically significant differences were observed in overall survival (OS) or progression-free survival (PFS), bone metastases were identified as a significant adverse prognostic factor, nearly doubling the risk of mortality (HR: 2.72, p < 0.001) regardless of KRAS subtype or co-mutation status. These findings underscore the importance of personalized treatment approaches tailored to the genetic profiles of patients with advanced NSCLC.