Objective To investigate the correlation of the ABO blood group distribution in patients with malignant rectal cancer and to assess the relative risk.

Methods A retrospective analysis was conducted on the ABO blood group data of 1 021 patients with rectal malignant tumors, and the comparison with the ABO blood group data of 1 132 cases of non-rectal malignant tumor patients randomly selected during the same period was made. The distribution and correlation of ABO blood group in patients with rectal malignant tumors were studied and analyzed.

Results The difference in the distribution of ABO blood group between patients with rectal malignant tumors and those with non-rectal malignant tumors was statistically significant (P ＜ 0.05). Overall, the proportion of type A blood was relatively high. Type A blood might be a relative risk factor for rectal malignant tumors (OR = 1.285, 95% CI = 1.073–1.539, P ＜ 0.01), and type O blood proportion was low and might play a protective role (OR = 0.726, 95% CI = 0.602–0.876, P ＜ 0.01). Compared with non-rectal malignant tumors, the proportion of type A blood in male patients with rectal malignant tumors was higher, and the proportion of type O blood was lower (P ＜ 0.05); in women, the proportion of type B blood was higher, and the proportion of type O blood was lower (P ＜ 0.05).

Conclusions Rectal malignant tumors are related to ABO blood group. Type A blood may be a relative risk factor, and type O blood may play a protective role. Male patients accord with overall distribution characteristics, while for female patients, type B blood may be a relative risk factor, and type O blood may play a protective role.