A tailored approach for endoscopic treatment of small rectal neuroendocrine tumor

Risk factors for residual tumors in histologically incompletely resected rectal neuroendocrine tumors

BACKGROUND

Rectal neuroendocrine tumors (r-NETs) are often misidentified as polyps, leading to inappropriate endoscopic treatment and incomplete resection.

AIMS

This study investigated the occurrence and risk factors of residual r-NETs following salvage local resection (SLR) after incomplete resection.

METHODS

The medical records of 95 patients who underwent SLR for histologically incompletely resected (R1/Rx-resected) r-NETs referred from other hospitals between January 2020 and August 2023 were analyzed.

RESULTS

The residual r-NET rate was 48.4 % (46/95), varying according to the primary resection method: cold forceps polypectomy (CFP), 70.0 % (21/30); conventional polypectomy or endoscopic mucosal resection (EMR), 41.7 % (25/60); and modified EMR or endoscopic submucosal dissection, 0 % (0/5). The residual r-NET rate was 65.7 % for endoscopically incomplete primary resection versus 0 % for endoscopically complete primary resection. Upon multivariate analysis, endoscopically suspected remnant tumors before SLR (odds ratio [OR], 15.56; 95 % confidence interval [CI], 2.94-82.35, p = 0.002) and the use of CFP for primary resection (OR, 3.60; 95 % CI, 1.02-14.52, p = 0.043) were associated with residual r-NETs after SLR.

CONCLUSION

Salvage resection should be considered for R1/Rx-resected r-NET cases with risk factors for residual tumors to lower the likelihood of recurrence.

Short-term outcomes of endoscopic resection for colorectal neuroendocrine tumors: Japanese multicenter prospective C-NET STUDY

OBJECTIVES

The incidence of colorectal neuroendocrine tumors (NETs) has increased with colorectal cancer screening programs and increased colonoscopies. The management of colorectal NETs has recently shifted from radical surgery to endoscopic resection. We aimed to evaluate the short-term outcomes of various methods of endoscopic resection for colorectal NETs.

METHODS

Among those registered in the C-NET STUDY, patients with colorectal NETs who underwent endoscopic treatment as the initial therapy were included. Short-term outcomes, such as the en bloc resection rate and R0 resection (en bloc resection with tumor-free margin) rate, were analyzed based on treatment modalities.

RESULTS

A total of 472 patients with 477 colorectal NETs received endoscopic treatment. Of these, 418 patients with 421 lesions who met the eligibility criteria were included in the analysis. The median age of the patients was 55 years, and 56.9% of them were men. The lower rectum was the most commonly affected site (88.6%), and lesions <10 mm accounted for 87% of the cases. Endoscopic submucosal resection with a ligation device (ESMR-L, 56.5%) was the most common method, followed by endoscopic submucosal dissection (ESD, 31.4%) and endoscopic mucosal resection using a cap (EMR-C, 8.5%). R0 resection rates <10 mm were 95.5%, 94.8%, and 94.3% for ESMR-L, ESD, and EMR-C, respectively. All 16 (3.8%) patients who developed treatment-related complications could be treated conservatively. Overall, 23 (5.5%) patients had incomplete resection without independent clinicopathological risk factors.

CONCLUSION

ESMR-L, ESD, and EMR-C were equally effective and safe for colorectal NETs with a diameter <10 mm.

Endoscopic treatments for rectal neuroendocrine tumors: a systematic review and network meta-analysis

BACKGROUND

Conventional endoscopic mucosal resection (cEMR), EMR with a transparent cap, EMR using a ligation device (EMR-L), EMR after circumferential precutting (EMR-P), and endoscopic submucosal dissection (ESD) have been used for resecting rectal neuroendocrine tumors (r-NETs). However, there is no consensus regarding which is the best treatment. This study aimed to compare the outcomes of the aforementioned 5 techniques for resecting r-NETs by network meta-analysis.

METHODS

Electronic databases (PubMed, Cochrane Library, Embase, Ovid Medline, and Web of Science) were systematically searched to include relevant studies published from inception to September 1, 2023. The en bloc resection rate, histologic complete resection rate, positive lateral margin rate, positive vertical margin rate, adverse events rate, and procedure time were compared.

RESULTS

A total of 27 studies with a total of 2112 r-NETs were included, and the mean diameter of tumors was 6.24 mm. Pairwise meta-analysis showed that EMR-L and ESD had higher en bloc resection and histologic complete resection rates and lower positive vertical margin rate than those of cEMR in resecting r-NETs. Compared with ESD, EMR-L and EMR-P achieved similar resection rates and significantly shortened the procedure time without increasing adverse events. The network meta-analysis evaluated the surface under the cumulative ranking curves and revealed that EMR-L was the best modality for treating r-NETs considering the comprehensive results of the en bloc resection rate, histologic complete resection rate, positive lateral margin rate, positive vertical margin rate, adverse events rate, and procedure time.

CONCLUSION

EMR-L should be recommended as the first-line endoscopic treatment for small r-NETs.

Molecular typing and mutational characterization of rectal neuroendocrine neoplasms

BACKGROUND

Rectal neuroendocrine neoplasms (NENs) are rare neoplasms with limited understanding of its genomic alterations and molecular typing.

METHODS

The paraffin-embedded tissue specimens of 38 patients with rectal NENs after surgery were subjected to whole gene sequencing (WGS), and mutation profilings were drawn to identify high-frequency mutation genes, copy-number variations (CNVs), tumor mutation burden (TMB), signal pathways, mutation signatures, DNA damage repair (DDR) genes, and molecular types. The differences of mutated genes and signaling pathways in different pathological grades and metastatic/non-metastatic groups were compared. It helped to search for potential targets.

RESULTS

C > T and T > C transitions are the most common base substitutions in rectal NENs. DNA mismatch repair deficiency, DNA base modifications, smoking and exposure to ultraviolet light might play a role in the occurrence of rectal NENs. DAXX, KMT2C, BCL2L1, LTK, MERTK, SPEN, PKN1, FAT3, and LRP2 mutations were found in only low-grade rectal NETs, whereas APC, TP53, NF1, SOX9, and BRCA1 mutations were common in high-grade rectal NECs/MiNENs. These genes helped in distinguishing poorly-differentiated or well-differentiated rectal NENs. Alterations in P53, Wnt and TGFβ signaling pathways were more pronounced in rectal NECs and MiNENs. Alterations in Wnt, MAPK and PI3K/AKT signaling pathways promoted metastases. Rectal NENs were classified into two molecular subtypes by cluster analysis based on the mutant genes and signaling pathways combined with clinicopathological features. Patients with mutations in the LRP2, DAXX, and PKN1 gene showed a trend of well-differentiated and early-stage tumors with less metastasis (p = 0.000).

CONCLUSIONS

This study evaluated risk factors for regional lymphatic and/or distant metastases, identified high-frequency mutated genes, mutation signatures, altered signaling pathways through NGS. Rectal NENs were divided into two molecular types. This helps to evaluate the likelihood of metastasis, formulate follow-up strategies for patients and provide a target for future research on precision treatment of rectal NENs. PARP inhibitors, MEK inhibitors, mTOR/AKT/PI3K and Wnt signaling pathway inhibitors may be effective drugs for the treatment of metastatic rectal NENs.

Colorectal Neuroendocrine Neoplasms: Areas of Unmet Need

The subject of colorectal neuroendocrine neoplasms (NENs), subdivided into well-differentiated NENs, termed neuroendocrine tumours (NETs; grade (G) 1 and 2), and poorly differentiated NENs, termed neuroendocrine carcinomas (NECs; G3) according to the 2010 World Health Organisation (WHO) classification, has arguably not had as much attention or study as NENs occurring in other sites. Colorectal NETs and NECs are however easier to study than many others since they are usually not difficult to remove and are increasingly detected because of intensified colorectal cancer screening and surveillance programmes. Colorectal NETs and NECs show site-specific heterogeneity with variable behaviour and different therapeutic options; these various aspects provide unique challenges. Because of bowel cancer screening programmes, colorectal NENs, like conventional adenocarcinomas, may be diagnosed at a stage that is associated with improved survival. In this article we intend to describe and define areas of unmet needs relating to the epidemiology, classification, pathology, diagnosis and therapy of colorectal NETs (including NETs G3), colorectal NECs, and finally, mixed adeno-neuroendocrine carcinomas (MANECs) by reviewing and discussing the relevant literature.

Role of endoscopic submucosal dissection in treatment of rectal gastroenteropancreatic neuroendocrine neoplasms

INTRODUCTION

A significant rise in incidence of rectal gastroenteropancreatic neuroendocrine neoplasms (GEP-NENs) has been observed in the last decade. Most detected gastroenteropancreatic neuroendocrine tumors (GEP-NETs) are well differentiated and less than 2 cm in diameter. Endoscopic submucosal dissection (ESD) is a new method for endoscopic treatment of such tumors, difficult to resect by conventional endoscopic techniques and thus subject to surgical treatment.

AIM

To present the results of the endoscopic treatment of GEP NET tumors in the rectum using ESD in single academic center.

MATERIAL AND METHODS

From June 2013 to April 2014, 4 cases of GEP-NET in the rectum were treated by ESD in our center. Effectiveness of dissection, complications and tumor recurrence after 3 months of treatment were then retrospectively investigated.

RESULTS

The group contained 2 patients with primary rectal GEP-NET (1 male, 1 female; age range: 48-60 years) and 2 with scars after incomplete polypectomy of rectal GEP-NET (1 male, 1 female; 61-65 years). Primary rectal GEP-NET diameters were 0.6 cm and 1.5 cm. Scar resection specimen diameters were 0.7 cm and 1 cm. Mean resection time was 28 min. The en bloc resection rate was 100% (2 of 2) and the histologically complete resection was confirmed in both cases. No foci of neuroendocrine neoplasia were reported in dissected scars. No complications were observed. After 3 months, 3 patients underwent follow-up colonoscopy - no local recurrence was reported.

CONCLUSIONS

Endoscopic submucosal dissection of rectal GEP-NET should be recommended as a treatment of choice when dealing with lesions over 1 cm in diameter without invasion of the muscle layer. Due to technical difficulties, performing this procedure should be reserved for centers with appropriately trained endoscopic staff.

Short- and long-term outcomes of endoscopic resection of rectal neuroendocrine tumours: analyses according to the WHO 2010 classification

OBJECTIVE

Although the World Health Organisation (WHO) defined a novel classification of gastroenteropancreatic neuroendocrine tumours (NETs) in 2010, indications for endoscopic resection of rectal NETs in the guidelines were based on evidence accumulated for carcinoid tumours defined by a previous classification. This study was designed to clarify indications for endoscopic resection of rectal NETs corresponding to the new WHO classifications.

MATERIAL AND METHODS

One hundred-seventy rectal NETs resected endoscopically from April 2001 to March 2012 were histologically re-classified according to the WHO 2010 criteria. The clinicopathological features of these lesions were analysed, and the short- and long-term outcomes of endoscopic resection were evaluated.

RESULTS

Of the 170 rectal NETs, 166 were histopathologically diagnosed as NET G1 and four as NET G2. Thirty-eight tumours (22.4%) were positive for lymphovascular invasion, a percentage higher than expected. Although the curative resection rate was low (65.3%), en bloc (98.8%) and complete (85.9%) resection rates were high. Modified endoscopic mucosal resection (88.0%) and endoscopic submucosal dissection (92.2%) resulted in significantly higher complete resection rates than conventional endoscopic mucosal resection (36.4%). No patient experienced tumour recurrence, despite the low curative resection rate.

CONCLUSION

Despite the low curative resection rate, prognosis after endoscopic resection of rectal NETs was excellent. Prospective large-scale, long-term studies are required to determine whether NET G2 and tumours >1 cm should be included in the indication for endoscopic resection and whether tumours with lymphovascular invasion can be followed up without additional surgery.

Endoscopic treatments for rectal neuroendocrine tumors smaller than 16 mm: a meta-analysis

OBJECTIVE

Endoscopic mucosal resection (EMR), including conventional EMR (c-EMR) and modified EMR (m-EMR), was applied to remove small rectal neuroendocrine tumors (NETs). We aim to evaluate treatment outcomes of endoscopic submucosal dissection (ESD), m-EMR and c-EMR for rectal NETs <16 mm.

METHODS

The PubMed, Cochrane Library and Elsevier Science Direct were searched to identify eligible articles. After quality assessment and data extraction, meta-analysis was performed. The main outcomes were complete resection rate, overall complication rate, procedure time and local recurrence rate.

RESULTS

Compared with c-EMR, ESD could achieve higher complete resection rate (OR = 4.38, 95%CI: 2.43-7.91, p < 0.00001) without increasing overall complication rates (OR = 2.21, 95%CI: 0.56-8.70, p = 0.25). However, ESD was more time-consuming than c-EMR (MD = 6.72, 95%CI: 5.84-7.60, p < 0.00001). Compared with m-EMR, ESD did not differ from m-EMR in complete resection and overall complication rates (OR = 0.80, 95%CI: 0.51-1.27, p = 0.34; OR = 1.91, 95%CI: 0.75-4.86, p = 0.18, respectively). However, ESD was more time-consuming than m-EMR (MD = 12.21, 95%CI: 7.78-16.64, p < 0.00001). Compared with c-EMR, m-EMR could achieve higher complete resection rate (OR = 4.23, 95%CI: 2.39-7.50, p < 0.00001) without increasing overall complication rate (OR = 1.07, 95%CI: 0.35-3.32, p = 0.90). Moreover, m-EMR was not time-consuming than c-EMR (MD = 2.01, 95%CI: -0.37-4.40, p= 0.10). The local recurrence rate was 0.84% (9/1067) during follow-up.

CONCLUSIONS

Both ESD and m-EMR have great advantages over c-EMR in complete resection rate without increasing safety concern while m-EMR shares similar outcomes with ESD for rectal NETs <16 mm. The results should be confirmed by well-designed, multicenter, randomized controlled trials with large samples and long-term follow-ups from more countries.

Early diagnosis and treatment of gastrointestinal neuroendocrine tumors

The aim of the present retrospective analysis on the macroscopic appearance and pathological characteristics of gastrointestinal neuroendocrine tumors (NETs) was to investigate methods for their early diagnosis and treatment. A total of 78 patients were divided into submucosal NET and deeper invasion NET groups, according to the depth of tumor invasion exhibited by the patients. The clinicopathological characteristics and survival time of the NET patients were analyzed and compared. The pathological characteristics of the submucosal NETs group were investigated according to the diameter of the tumor (≤5.0 mm, 5.1-10.0 mm or >10.0 mm). The depth of invasion at diagnosis was observed to significantly correlate with histopathological classification, diameter of the tumor, macroscopic appearance, growth pattern, lymphatic-vascular involvement, lymph node (LN) metastasis and distant metastasis. In the submucosal NETs group, high-grade tumors with lymphatic or venule invasion and distant metastasis were associated with an increased risk of nodal metastases. In patients with minute tumors (≤5.0 mm), no lymphatic-vascular involvement, LN or distant metastasis was observed. By contrast, patients with tumors measuring 5.1-10.0 mm in diameter exhibited high lymphatic-vascular involvement and LN metastasis rates (46.2 and 30.8%, respectively). Survival time was significantly longer in patients with submucosal NETs compared with deeper invasion NETs and in patients with NET G1 and NET G2 compared with NEC. The results of the present study indicate that gastrointestinal submucosal NETs are closely associated with a slightly elevated macroscopic type, low-grade tumors and a small diameter. These features may contribute to early diagnosis of gastrointestinal NETs. Therefore, a tumor diameter of <5.0 mm, with slightly elevated macroscopic appearance may indicate an absolute requirement for endoscopic resection, while tumors measuring 5.1-10.0 mm in diameter must be considered carefully.