Appendiceal Neuroendocrine Tumors: Prognostic Role of Mesoappendiceal Invasion and Implications for Recommending...

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.

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.

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).

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.