There are no strategies to predict a patient's response to therapy. In a previous report, we classified Japanese patients into four groups according to the incidence of HLA antigens, by using the quantification method III. We examined the HLA antigens of patients before surgery and evaluated their outcome according to the HLA classification by this quantification method. We also reported that HLA-oriented therapy was better than old fashioned therapy. The aim of the present study was to evaluate whether HLA classification is useful in the treatment of individual cancer patients, by using a consecutive retrospective study series of 1932 patients from Jan 1977 to May 1996 and a consecutive prospective study series of 582 patients from Jun 1996 to Aug 2005, all of whom received gastrectomies. There were significant differences between male patients who agreed to get the recommended therapy (the patients in agreement) and those who did not (the patients in disagreement), those with lymph node metastasis, those with undifferentiated adenocarcinoma, and those in stage 3A. Moreover, stage 2 and 3A patients benefitted from HLA-oriented therapy in a prospective study. In conclusion, our results showed that it is beneficial to examine HLA antigens preoperatively, that HLA-oriented therapy is promising, and that we must determine predictive factors for response to therapy in the future. We concluded that HLA antigens are promising predictive markers for cancer treatment.