Introduction. The study of the possible impact of the blood group system ABO and other antigenic systems of red blood cells for cancer patients is currently directed at a number of distinct paths, including the study of changes in the expression of a group of antigens in tumors; the appearance of new antigens on tumor cells; the risk of developing tumors depending on the blood group; the possible infl uence of blood group on the prognosis of the disease, etc.Aim — to examine the current state of the problem of the relationship between blood groups and cancer.Main findings. There is evidence that cancer is less common in people with blood type O than in people with other blood groups of the ABO system. According to other data, this dependence is noted only for some types of cancer. In general, the results of work on this topic can be assessed as insuffi cient and sometimes contradictory.