Appendiceal Neuroendocrine Tumors: Prognostic Role of Mesoappendiceal Invasion and Implications for Recommending Right Hemicolectomy versus Simple Appendectomy.

Background: Current guidelines are conflicting as to whether mesoappendiceal invasion (MAI) among patients with appendiceal neuroendocrine tumors (aNETs) warrants right hemicolectomy (RHC), especially in the absence of other concomitant high-risk features.

Methods: Patients who underwent resection of aNETs were identified in the National Cancer Database. Patients with pT3 aNETs (i.e. size > 4 cm or MAI/subserosal invasion [SI]+) were further stratified as pT3a (size ≤ 4 cm, + MAI/SI) or pT3b (size > 4 cm, ± MAI/SI). The association of MAI/SI with nodal metastasis (pN+) relative to the presence/absence of other risk factors was examined. The prognostic impact of the extent of resection (i.e. RHC vs. appendectomy) among patients with MAI/SI was assessed.

Results: Among 4819 patients who underwent resection for aNETs, 1662 had pT3 tumors, of which 1309 (78.7%) were pT3a and 353 (21.3%) were pT3b. The overall incidence of pN+ disease was 7.5%, and varied by American Joint Committee on Cancer (AJCC) pT stage (pT1: 0.9%; pT2: 9.2%; pT3: 8.5%; pT4: 29.8%; p < 0.001). pT3a stage was less frequently associated with pN+ disease compared with pT3b disease (6.8% vs. 14.7%; p = 0.02). In the absence of other established risk factors, the presence of MAI/SI alone was associated with a low probability of pN+ (3.4%). The 3-year overall survival among patients with pT3a aNETs was comparable following RHC versus simple appendectomy (92.7% vs. 95.2%; p = 0.43).

Conclusions: Among patients with resected aNETs, MAI/SI alone in the absence of other established risk factors was associated with a low likelihood of nodal metastasis and equivalent long-term outcomes regardless of the extent of surgical resection. The presence of MAI/SI alone should not be an indication for RHC.