Prognosis of incompletely resected small rectal neuroendocrine tumor using endoscope without additional treatment

Abstract

Background In recent years, the incidence of rectal neuroendocrine tumors (NET)s has markedly increased due to the widespread use of screening colonoscopy. However, many patients are referred from local clinics after undergoing conventional endoscopic mucosal resection (EMR) for polyps without perceived NET, with a pathological report of incomplete resection. We evaluated the prognosis of incompletely resected small rectal NET without additional endoscopic resection for small rectal NET less than 10 mm in diameter present within the submucosal layer showing good prognosis, due to its rare metastatic potential. Methods We retrospectively reviewed patients from 2008 to 2018 at a single center who had had small rectal NET (located in the rectum from the anal verge to 20 cm in proximity) and had undergone ‘incomplete resection’ using endoscopy with a positive deep margin or with a very small safe deep margin (< 100 um). A small rectal NET was defined as a tumor ≤ 10 mm in diameter, without lymph node nor distant metastasis, and with low grade (G1) according to the WHO grading system. Results Of 267 patients who were diagnosed with small rectal NET, 77 were diagnosed with incomplete resection or possible remnant NET. Of those, 55 patients (55/77, 71.4%) were referred from local clinics post EMR diagnosed as polyps. The rate of histologically incomplete resection was highest in endoscopic submucosal dissection (11/21, 52.4%) and lowest in surgical resection (0/9, 0%), while endoscopic submucosal resection with band ligation showed an incomplete resection rate of 4.4% (5/113). After exclusion of 36 patients, namely 21 patients had undergone additional surgical (n = 6) or endoscopic (n = 15) resection and 25 patients who were lost during the follow-up period of 2 years, 31 patients had undergone surveillance with endoscopic evaluation or either a biopsy or radiological evaluation for distant metastasis during a median follow-up duration of 2 years. None of the incompletely resected small rectal NET patients showed local or distant metastasis. Conclusion Incomplete resection of small rectal NET with G1 grade has a good prognosis without additional treatment.

Risk factors and clinical outcomes of incomplete endoscopic resection of small rectal neuroendocrine tumors in southern China: a 9-year data analysis

“…The incidence of RNETs has rapidly increased over the past few years along with the increase in screening by colonoscopy [ 18–20 ]. However, the CR rates of RNETs treated by endoscopy varied widely as reported by different studies, ranging from 39% to 85% [ 8 , 11 , 16 , 21 ]. The overall CR rate of RNETs is reportedly only 84.08% even after the advanced endoscopic technique of ESD [ 22 ].…”

“…In clinical practice, a large proportion of patients with IR lesions refused salvage treatment for fear of salvage-therapy-related complications and economic burden. It has been reported that 72.7% (56 of 77) of those with incompletely resected small RNETs refused salvage treatment [ 16 ]. For such small IR lesions without additional therapy, it was still unclear whether regular follow-up is safe and feasible.…”

Treatment of localized well-differentiated rectal neuroendocrine tumors: A focused review

“…[54,55] In another study of 77 G1 NET patients with positive surgical margins, 31 patients did not receive additional treatment and did not develop recurrence. [56]…”

“…In another study of 77 G1 NET patients with positive surgical margins, 31 patients did not receive additional treatment and did not develop recurrence. [56] Japanese guidelines recommend additional local excision for positive margins after endoscopic resection, even for NET G1 < 1 cm. [8] In Europe and the United States, additional treatment is recommended when invasion of the muscular propria layer is observed or when G2 NET is observed.…”

European Neuroendocrine Tumor Society (ENETS) 2023 guidance paper for colorectal neuroendocrine tumours

“…49 Some units would recommend a watch-and-wait policy but there is a small risk of recurrence and the patient will need long term follow-up. There are large series from South Korea 60,61 where this disease is very common, and it seems clear that up to 2 years the recurrence rate is close to 0. This does not necessarily mean that the recurrence rate is 0 for ever and if watch and wait is adopted we recommend flexible sigmoidoscopy at F I G U R E 1 Diagnostic and therapeutic algorithm for patients with rectal neuroendocrine tumours (NET).…”