Abstract: Objective To observe the sensitizing effect and safety of thalidomide on preoperative intensity modulated radiotherapy （IMRT） for stage Ⅱ／Ⅲ rectal cancer. Methods  From January 2016 to December 2017， 60 patients with stage Ⅱ／Ⅲ rectal cancer receiving preoperative radiotherapy were randomly divided into experimental group （n=30） and control group （n=30）. Both 2 groups received IMRT combined with capecitabine oral concurrent chemotherapy before operation. On this basis， the experimental group was given thalidomide 100 mg／d every night in the first week of radiotherapy， and the second week was added to maintain the target dose of 200 mg／d until the end of radiotherapy. Radical resection of rectal cancer was performed at 6-8 weeks after radiotherapy. The changes of serum vascular endothelial growth factor （VEGF） before and after radiotherapy， the variations of tumor stage， the R0 resection rate， the rate of anus preserving and the pathologic regression degree of the tumor were compared between the two groups. The incidence of acute radiation injury during radiotherapy was recorded and the adverse reactions of thalidomide were evaluated. Results Before radiotherapy， the levels of serum vascular endothelial growth factor in experimental group and control group were （542.47±107.06）pg／ml and （536.36±97.32）pg／ml， with no significant difference （P＞0.05）. The levels of serum vascular endothelial growth factor （VEGF） in the experimental group and the control group were 419.61±77.80）pg／ml and（503.52±87.31）pg／ml after radiotherapy （P＜0.05）. The level of serum VEGF before and after radiotherapy in the experimental group was significantly different （P＜0.05）. After treatment， the T and N staging rate， anal preservation rate， tumor pathological complete remission rate and good rate of tumor regression in the experimental group were significantly higher than those in the control group （P＜0.05）. Nine patients in the experimental group developed nausea and vomiting， 22 patients developed radiation proctitis， and 28 patients in the control group and 30 patients in the control group， respectively. In the experimental group， dizziness and lethargy occurred in 16 cases， while only 6 cases in the control group. Conclusion Thalidomide combined with preoperative IMRT in the treatment of stage Ⅱ／Ⅲ rectal cancer has a synergistic effect， which can significantly reduce the tumor stage， improve the complete pathological remission rate and the good rate of tumor regression. More patients have the chance of anus preservation， and the synergistic mechanism may be related to the reduction of the level of VEGF to regulate angiogenesis. It can reduce the incidence of nausea， vomiting and radiation proctitis.

Key words:

Rectal cancer')">"> Rectal cancer, Thalidomide, Preoperative radiotherapy, Sensitization effect