Objective To investigate the risk factors of liver metastasis in patients with middle and low rectal cancer of Ⅱ–Ⅲ stage after preoperative short course radiotherapy combined with chemotherapy. MethodsThe clinical data of 89 patients with middle and low rectal cancer of Ⅱ–Ⅲ stage admitted to the Dongnan Hospital of Xiamen University from January 2019 to June 2020 were retrospectively analyzed. All patients were treated with short-course radiotherapy combined with chemotherapy before operation. The risk factors of postoperative liver metastasis were analyzed by multivariate logistic regression. ResultsThe 89 patients were followed up for 7–53 months, with a median follow-up time of 33 months. During the follow-up period, 25 patients developed liver metastasis, the onset time was 7–35 months, and the median time of liver metastasis was 17 months. Among them, 5 patients (5.6%) developed liver metastasis in the first year after surgery, 15 patients (16.8%) developed liver metastasis at the second year after surgery, 5 patients (5.6%) developed liver metastasis at the 3rd year after surgery. Multivariate logistic regression results showed that lymph node metastasis [OR=3.550, 95%CI (1.425, 8.953), P=0.041], vascular invasion [OR=3.335, 95%CI (1.011, 11.001), P=0.048], maximum tumor diameter ≥5 cm [OR=4.477, 95%CI (1.273, 15.743), P=0.019], and peri-tumor diameter ≥1/2 [OR=4.633, 95%CI (1.387, 15.475), P=0.013] were risk factors for liver metastasis. ConclusionsLymph node metastasis, vascular invasion, maximum tumor diameter ≥5 cm, and circumferential tumor diameter ≥1/2 are risk factors for liver metastasis in patients with middle and low rectal cancer of Ⅱ–Ⅲ stage after preoperative short course radiotherapy combined with chemotherapy.