OBJECTIVETo investigate the intramural lateral spread distance in low rectal cancer in order to provide basis for safety lateral resection margin of pull-through conformal resection (PTCR).

METHODSThe patients with low rectal cancer who received low anterior resection or abdominal-perineal resection in Changhai Hospital from December 2015 to March 2016 were enrolled and Surgical specimens were collected. After the specimens were fixed in 10% formaldehyde for 24 hours, a piece of tissue that was 1.5 cm in length and 0.5 cm in width from the edge of tumor was cut. The tissue was obtained in the direction of 3, 5, 7 and 9 o'clock clockwise. The distance of intramural lateral spread was measured in the specimens and the risk factors were analyzed.

RESULTSA total of 83 specimens were collected and the overall proportion of intramural lateral spread was 71.1%(59/83). The rate of lateral spread from 3 to 9 o'clock was 34.9%(29/83), 26.5%(22/83), 32.5%(27/83) and 37.3%(31/83) respectively, and the difference was not statistically significant(χ=2.444 9, P=0.485 3). The median distance of lateral spread in each direction was all 0 mm and the quartile range was 1 mm, 0.5 mm, 0.55 mm and 1 mm respectively. The 5th percentile (P5) of each direction was all 0 mm and the 95th percentile(P95) of each direction was 2.5 mm, 1.6 mm, 2.6 mm, 2.5 mm, respectively and the difference was not statistically significant either(χ=5.331 0, P=0.148 9). The rate of lateral spread of T1, T2, T3 and T4 was 0/4, 58.3%(14/24), 83.0%(44/53) and 1/2 respectively, and there was significant difference(P=0.005 0). The multivariate analysis indicated that T stage (P=0.002 2, OR=3.741, 95% CI: 1.606-8.716) was the risk factor of intramural lateral spread.

CONCLUSIONSThe intramural lateral spread does exist in low rectal cancer and T stage is the risk factor of lateral spread. The lateral resection margin should be 5 mm from the tumor edge at least when PTCR is performed.