The present invention provides a method and a reagent for detecting a digestive organ cancer, gastric cancer, colorectal cancer, pancreatic cancer, or biliary tract cancer patient by analyzing genes with expression levels (in peripheral blood) that vary in association with digestive organ cancer, gastric cancer, colorectal cancer, pancreatic cancer, or biliary tract cancer cases, compared with normal healthy subjects. Specifically, the method for detecting a digestive organ cancer, gastric cancer, colorectal cancer, pancreatic cancer, or biliary tract cancer patient based on expression profiles comprises obtaining the expression profile of at least one gene selected from the group consisting of probes corresponding to genes with expression levels (in peripheral blood) that vary in digestive organ cancer, gastric cancer, colorectal cancer, pancreatic cancer, and biliary tract cancer cases, compared with normal healthy subjects. The reagent for detecting digestive organ cancer, gastric cancer, colorectal cancer, pancreatic cancer, or biliary tract cancer contains nucleotides or partial sequences thereof consisting of the nucleotide sequence of at least one gene selected from the group consisting of probes with expression levels that vary in digestive organ cancer, gastric cancer, colorectal cancer, pancreatic cancer, or biliary tract cancer, or nucleotides containing sequences complementary thereto.