Abstract: Objective To explore the effect of peripheral blood cluster of differentiation 8-positive cells （CD8+） T lymphocyte level and expression of circulating tumor cells (CTC) on the prognosis of stage Ⅲ colorectal cancer (CRC)patients undergoing adjuvant radiochemotherapy after radical surgery. 
Methods We selected 156 CRC patients undergoing adjuvant radiochemotherapy after radical surgery in our hospital as research subjects. They were followed up for 6 months.According to presence of recurrence during the follow-up period, they were divided into non-rercurrence group (n=112) and recurrence group (n=44). T lymphocyte subsetlevel and CTC expression levels were detected in patients at 1 d after surgery, to explore the relationship between the positive rate of CTC expression and the clinicopathological characteristics of patients, and to investigate the predictive value of the above indicators for prognosis of patients. 
Results Compared with non-recurrence group, recurrence group had lower CD3+, CD4+, and CD4+/CD8+ levels, but higher CD8+ levels (P＜0.05). CTC expression in the peripheral blood of patients was determined, and CTC count was (2.56±0.87) in non-recurrence group and (6.68±2.74) in recurrence group, suggesting significant differences (t=9.782, P＜0.05). CTC expression of patients was not related to gender, age, lymph node metastasis, or degree of tissue differentiation of patients (P＞0.05). Receiver operating characteristic (ROC) curve was used to analyze the predictive value of T lymphocyte subset levels and CTC expression for recurrence, and the area under the curve (AUC) of CD3+, CD4+, CD8+, CD4+/CD8+ and CTC expression was 0.852, 0.703, 0.712, 0.747, and 0.920, respectively. The AUC of the combined application of the above indexes in predicting the recurrence of the patients was 0.954. 
Conclusion Low expression of CD3+, CD4+, CD4+/CD8+, and high expression of CD8+ and CTC in patients with stage Ⅲ CRC undergoing adjuvant chemoradiotherapy after radical surgery will increase the postoperative recurrence rate, and the combined detection of all indicators has certain predictive value for the prognosis of patients. 

Key words: colorectal neoplasms, CD8+ T lymphocytes, circulating tumor cells