Early detection of tumors is a major determinant of survival of patients suffering from tumors, including gastric tumors. Members of the GTM gene family, in particular the GTM gene known as serine or cysteine proteinase inhibitor clade H ("SERPINH1"), can be over-expressed in gastric tumor tissue and other tumor tissue, and thus can be used as markers for gastric and other types of cancer. GTM proteins can be released from cancer cells, and can reach sufficiently high concentrations in the serum and/or other fluids to permit their detection. Thus, methods and test kits for detection and quantification of GTM can provide a valuable tool for diagnosis of gastric cancer.