Abstract: Objective To investigate the significance of the detection of circumferential resection margin(CMR) after rectal cancer excision for the treatment
and prognosis of rectal cancer,and to provide basis for  improving the survival rate of patients with mid-low rectal cancer.
Methods 78 patients with mid-low rectal cancer were operated following the principles of total mesorectal excision(TME).The specimens were made into large slices stained by HE and the positive rate of circumferential margin invasion (CMI)  of the specimen was detected.Then the patients were followed-up,and the  mortality rates,the local recurrence rates and the postoperative metastasis rates of the CRM positive and CRM negative patients were compared.
ResultsThe patients were all followed-up and the follow-up time was  mean 17  months.The  positive rate of CMI was 25.64% (20/78).
 The   positive rates of T1 and T2 tumor (0 % and 0 %) were lower than that of T3 tumor (29.85% ,20/67,P<0.05).The positive rates of CMI in well differentiated and moderately differentiated tumor were 12.50%(1/8) and 16.36%(9/55),respectively,which were lower than that in poorly differentiated tumor(66.67%,10/15,
P<0.05). The  positive rate of CMI in lymph node N0 group (12.77%，6/47) was lower than those in N1 and N2  groups(40.00%，8/20； 54.55%，6/11,P<0.05).The positive rate of CMI in the specimens with the distance from the lower edge of  tumor to the dentate line≤5 cm  (48.15%,13/27) was higher than that in the specimens with the distance >5 cm (13.73%,7/51,P<0.05). During the 17 months of follow-up,10  cases died,in which there were 6 cases of  CMI.Postoperative local recurrence was found in  4 cases of positive  CMI.Moreover,there were 6 cases of CMI in 10 cases of postoperative distant metastasis.There were significant differences of the  mortality,local recurrence rate and postoperative metastasis rate between CRM positive
 (30.0%，20.0%，and 30.0%) and CRM negative patients (6.9%，0%， and 6.9%)(P<0.05).Conclusion CRM should be routinely detected
 in the patients with  mid-low rectal cancer after operation.The mortality,the local recurrence rate and the postoperative metastasis rate of CMI patients are significantly increased;chemotherapy and radiotherapy should be applied in order to reduce the local recurrence rate and the mortality.

Key words: rectal neoplasms, circumferential resection margin, circumferential margin invasion, slice, follow-up