The development of antitumor MAbs has led to the identification of many TAAs but no TSAs. It now seems unlikely that there are antigens exclusively associated with any tumor type. Nonetheless, there are numerous applications of the antitumor MAbs. They are used in serum assays to monitor tumor burden and in histologic assays to identify the tumor type. Initial attempts to use MAbs therapeutically have benefited some patients, but much work is needed to better understand the mechanism and to enhance this tumoricidal effect. Finally, the antitumor MAbs will allow biochemical and genetic analyses of the roles of TAAs in tumor progression.