KRAS mutations are causally linked to pro-tumor inflammation and identified as driving factors in tumorigenesis. Here, using multi-omics data gathered from a large set of patients, we showed that KRAS mutation was associated with a specific landscape of alternative mRNA splicing that connected to myeloid inflammation in intrahepatic cholangiocarcinoma (iCCA). Then, we identified a negative feedback mechanism in which the upregulation of interleukin 1 receptor antagonist (IL1RN)-201/203 due to alternative splicing confers vital anti-inflammatory effects in KRAS mutant iCCA. In KRAS mutant iCCA mice, both IL1RN-201/203 upregulation and anakinra treatment ignited a significant anti-tumor immune response by altering neutrophil recruitment and phenotypes. Furthermore, anakinra treatment synergistically enhanced anti-PD-1 therapy to activate intratumoral GZMB+ CD8+ T cells in KRAS mutant iCCA mice. Clinically, we found that high IL1RN-201/203 levels in KRAS mutant iCCA patients were significantly associated with superior response to anti-PD-1 immunotherapy.