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Somatostatin analogues have recently been used as therapeutic targets for metastatic or surgically unresectable gastroenteropancreatic (GEP) neuroendocrine tumors (NETs), and associated somatostatin receptor (SSTR) expression has been well demonstrated in most GEP NETs, with the exception of rectal NETs. SSTR2 immunohistochemical expressions were evaluated in 350 surgically or endoscopically resected rectal NETs and compared to clinicopathologic factors. SSTR2 expression was observed in 234 (66.9%) rectal NET cases and associated tumors with smaller size (p = 0.001), low pT classification (p = 0.030), low AJCC tumor stage (p = 0.012), and absence of chromogranin expression (p = 0.009). Patients with rectal NET and SSTR2 expression had significantly better overall survival than those without SSTR2 expression both by univariable (p = 0.006) and multivariable (p = 0.014) analyses. In summary, approximately two-thirds of rectal NETs expressed SSTR2. SSTR2 expression was significantly associated with favorable behavior and good overall survival in patients with rectal NETs. Furthermore, SSTR2 expression can be used as prognostic factors. When metastatic disease occurs, SSTR2 expression can be used a possible target for somatostatin analogues. [ABSTRACT FROM AUTHOR]

Background: Owing to an increased number of colonoscopy screenings, the incidence of diagnosed rectal neuroendocrine tumors (NETs) has also increased. Tumor size is one of the most frequently regarded factors when selecting treatment; however, it may not be the determinant prognostic variable. We aimed to evaluate oncological outcomes according to the treatment modality based on the size of rectal NETs. Methods: A retrospective analysis was performed on patients who were treated for rectal NETs between March 2000 and January 2016 at the Asan Medical Center, Seoul, Korea. Patients who underwent endoscopic removal, local surgical excision, and radical resection were included. The primary outcome was recurrence-free survival (RFS). Data were specified and analyzed following the 2019 World Health Organization classification (WHO). Results: A total of 644 patients were categorized under three groups according to the treatment modality used: endoscopic removal (n = 567), surgical local excision (n = 56), and radical resection (n = 21). Of a total of 35 recurrences, 27 were local, whereas eight were distant. The RFS rate did not differ significantly between the treatment groups in the same tumor-size group (≤ 1 cm group: P =.636, 1–2 cm group: P =.160). For T1 tumors, RFS rate was not different between local excision and radical resection (≤ 1 cm group: P =.452, 1–2 cm group: P =.700). Depth of invasion, a high Ki-67 index, and margin involvement were confirmed as independent risk factors for recurrence. Among patients treated with endoscopic removal, endoscopic biopsy was a significant factor for worse RFS (P <.001), while tumor size did not affect the RFS. Conclusion: The current guideline recommends treatment options according to tumor size. However, more oncologically important prognostic factors include muscularis propria invasion and a higher Ki-67 index. [ABSTRACT FROM AUTHOR]