Abstract The majority of sporadic human colorectal cancer is initiated by genetic loss or inactivation of tumor suppressor APC (Absent in Polyposis Coli). In addition to activation of beta-catenin signaling, we found that loss of APC results in upregulation of IL-6 signal transducer (IL6/gp130), thereby leading to activation of STAT3 and YAP, two transcription factors that make important contributions to colorectal tumorigenesis. In addition, APC loss results in deterioration of the intestinal epithelial barrier and immune homeostasis, barrier loss due to downregulation of genes encoding tight junction proteins, and suppression of mucin production. Together, such changes promote the invasion of inflammation-inducing colitogenic bacteria and their products. Loss of immune homeostasis is due to defective luminal transport of IgA dimers caused by loss of polyimmunoglobin receptor (PIgR) and CCL28, a chemokine responsible for recruitment of IgA-producing plasma cells. Defective luminal transport of IgA results in dysbiosis and over-representation of inflammation-causing bacteria that can accelerate colorectal tumor genesis through upregulation of IL-17 production. Citation Format: Michael Karin. Tumor-elicited inflammation in colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr SY19-01. doi:10.1158/1538-7445.AM2017-SY19-01
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