Variability in non-tumor areas of colorectal cancer patients as revealed by endoscopic intestinal step biopsies

A comprehensive endoscopic small and large intestinal untargeted step biopsy procedure was conducted to compare gene expression between the normal intestinal mucosa of healthy individuals and that of patients with colorectal tumors. From 78 participants (healthy individuals [n = 17], patients with colorectal conventional adenomas [n = 6], patients with Tis–T1 colorectal cancer [n = 41], patients with T2–4 colorectal cancer [n = 14]), biopsies of normal mucosa of the terminal ileum, right-sided colon (cecum and ascending colon), and left-sided colorectum (descending colon, sigmoid colon, and rectum) were obtained using a lower gastrointestinal endoscope. RNA was extracted from all samples, and total transcriptome sequencing was performed. Transcriptome data from 388 samples was analyzed. DNA was also extracted from tumor biopsy tissues and analyzed for whole-exome sequencing. In healthy individuals, gene expression differed significantly among the terminal ileum, right-sided colon, and left-sided colorectum, presumably linked to embryological factors. There were differences in gene expression in the normal mucosa in colorectal cancer patients, compared to healthy controls. Patients with tumors, especially T2–4 colorectal cancer, showed considerable variation in gene expression in non-tumor tissues, even in the terminal ileum distant from the tumor site. Based on endoscopic biopsies, the results imply cancer-predisposing conditions in seemingly normal tissues. The present study points to the importance of small intestine and cancer-predisposing conditions in the colon of colorectal cancer patients, with possible implications for developing novel immunotherapy and other therapeutic modalities.