Background:Carbon nanoparticles show significant lymphatic tropism and can be used to identify lymph nodes surrounding mid-low rectal tumors.In this study,we analyzed the effect of trans anal injection of a carbon nanoparticle suspension on the outcomes of patients with mid-low rectal cancer who underwent laparoscopic resection.Methods:We collected the data of 87 patients with mid-low rectal cancer who underwent laparoscopic resection between November 2014 and March 2015 at Cancer Hospital,Chinese Academy of Medical Sciences & Peking Union Medical College.For 35 patients in the experimental group,the carbon nanoparticle suspension was injected transanally into the submucosa of the rectum around the tumor 30 min before the operation;52 patients in the control group underwent the operation directly without the injection of carbon nanoparticle suspension.We then compared the operation outcomes between the two groups.Results:In the experimental group,the rate of incomplete mesorectal excision was lower than that in the control group,but no significant difference was found(2.9%vs.7.7%,P = 0.342).The distance between the tumor and the circumferential resection margin was 5.8 ± 1.4 mm in the experimental group and 4.8 ±1.1 mm in the control group(P = 0.001).The mean number of lymph nodes removed was 28.2 ± 9.4 in the experimental group and 22.7 ± 7.3in the control group(P = 0.003);the mean number of lymph nodes smaller than 5 mm in diameter was 10.1 ± 7.5and 4.5 ±3.7,respectively(P< 0.001).Three patients in the experimental group received lateral lymph node resection.Among the three patients,we retrieved three nodes(one stained node) from the first patient,three nodes(two stained nodes) from the second patient,and two nodes(no stained nodes) from the third patient.Conclusions:Injecting a carbon nanoparticle suspension improved the outcomes of patients who underwent laparoscopic resection for mid-low rectal cancer;it also improved the accuracy of pathologic staging.Moreover,for selected patients,this technique narrowed the scope of lateral lymph node dissection. Background: Carbon nanoparticles show significant lymphatic tropism and can be used to identify lymph nodes surrounding mid-low rectal tumors. In this study, we analyzed the effect of trans anal injection of a carbon nanoparticle suspension on the outcomes of patients with mid-low rectal cancer who underwent laparoscopic resection. Methods: We collected the data of 87 patients with mid-low rectal cancer who underwent laparoscopic resection between November 2014 and March 2015 at Cancer Hospital, Chinese Academy of Medical Sciences & Peking Union Medical College. For 35 patients in the experimental group, the carbon nanoparticle suspension was injected transanally into the submucosa of the rectum around the tumor 30 min before the operation; 52 patients in the control group underwent the operation directly without the injection of carbon nanoparticle suspension. We then compared the operation outcome between the two groups. Results: In the experimental group, the rate of incomplete mesorectal excis ion was lower than that in the control group, but no significant difference was found (2.9% vs.7.7%, P = 0.342). The distance between the tumor and the circumferential resection margin was 5.8 ± 1.4 mm in the experimental group and 4.8 ± 1.1 mm in the control group (P = 0.001). The mean number of lymph nodes removed was 28.2 ± 9.4 in the experimental group and 22.7 ± 7.3 in the control group (P = 0.003); the mean number of lymph nodes smaller than 5 mm in diameter was 10.1 ± 7.5 and 4.5 ± 3.7, respectively (P <0.001). Thhree patients in the experimental group received lateral lymph node resection. Among the three patients, we retrieved three nodes (one stained node) from the first patient , three nodes (two stained nodes) from the second patient, and two nodes (no stained nodes) from the third patient. Conclusions: Injecting a carbon nanoparticle suspension improved the outcomes of patients who underwent laparoscopic resection for mid-low rectal cancer; it also improved the accuracy of pathologic staging reover, for selected patients, this technique narrowed the scope of lateral lymph node dissection.