OBJECTIVETo assess the efficacy of full-thickness excision using transanal endoscopic microsurgery (TEM) in the treatment of rectal neuroendocrine tumors (NET).

METHODSClinicopathological and follow-up data of 90 rectal NET patients who underwent TEM between December 2006 and December 2016 at our department were retrospectively analyzed. TEM was performed as primary excision in 66 patients and as the second complete surgery because of suspected positive margin of samples after colonoscopic polypectomy in 24 patients.

RESULTSTEM was successfully performed in all the rectal NET patients, and in 10 patients(41.7%,10/24) among those undergoing the second excision, postoperative pathologic results showed remnant tumor. The mean diameter of all the tumors was (1.03±0.46) cm, and the mean tumor diameter of primary excision and secondary excision was (1.10±0.50) and (0.84±0.23) cm respectively (t=2.454, P=0.016). The mean distance from tumor low margin to anal verge was (7.7±1.8) cm for all the patients, and such distance for those undergoing primary excision and secondary excision was (7.4±1.7) cm and (8.4±1.8) cm respectively (t=2.233, P=0.028). Of all the patients, the mean intra-operative blood loss was (13.7±5.1) ml, and the mean operation time was (56.6±12.1) min. The intra-operative blood loss and operative time were similar in primary excision and secondary excision (both P>0.05). Histopathologically, both fundus and lateral margins of all the samples were negative. Of the 76 samples, cancer tissue developed outside the mucosal layer in 37 samples, infiltrated into the submucosal layer (pT1 stage) in 33 samples, and infiltrated into the muscular layer (pT2 stage) in 6 samples; 57 samples were classified as grade G1 and 19 samples were classified as grade G2, respectively. The operative complication rate was 6.7%(6/90). The mean postoperative hospital stay was (3.0±1.5) d. No recurrence was noted during the follow-up (median 3.9, 0.4 to 10.0 years).

CONCLUSIONSTEM can be the preferred option for complete removal of middle-upper small (<2 cm) rectal NET(G1-2). For rectal NET with incomplete resection by colonoscopic polypectomy, the secondary TEM can still obtain ideal efficacy even though operative difficulty increases.