The present invention provides biological markers associated with gastric cancer. In particular, the present invention provides a method of diagnosing gastric cancer (GC) in a subject, the method including: measuring an expression level of one or more proteins in the subject, wherein the one or more proteins are selected from the group consisting of vitamin D binding protein (VDBP), clusterin, insulin like growth factor binding protein complex acid labile subunit (IGFALS), and afamin; comparing the expression level of the or each protein in the subject to a reference expression level for the or each protein; and diagnosing GC in the subject on the basis of the comparison. On the basis of the identification of biological markers associated with gastric cancer, the present invention also provides a method of determining if a subject is susceptible to developing gastric cancer, a method of assessing progression of gastric cancer in a subject, a method for screening a candidate therapeutic agent useful for treating gastric cancer in a subject, and a kit for diagnosing gastric cancer in a subject.