Clinicopathological Features of Low-Grade Appendiceal Mucinous Neoplasms Confined to the Appendix.

Objective: To investigate the clinicopathological features and follow-up of low-grade appendiceal mucinous neoplasms (LAMNs) confined to the appendix.

Methods: The clinicopathological features, pathological primary tumor (pT) staging and follow-up of 22 patients with LAMNs confined to the appendix were analyzed retrospectively.

Results: Of 22 patients with LAMNs, 14 were pTis (eight pTis^m and six pTis^f), six were pT3, and two were pT4a. The appendiceal diameter was significantly larger for pTis^f than for pTis^m. The interval between first symptoms and surgery was longer for pTis^f than for pTis^m, but not significantly different. No significant differences were found between the pT stages and appendiceal diameter or in the interval between the first symptoms and surgery. Pathomorphologically, the epithelial structures were mainly flat (100%), undulating or scalloped (82%); a few showed filiform villous hyperplasia (46%), and seven (32%) had serrated lesions in the background. Diverticula may be associated with LAMNs, and the location of acellular mucin caused by diverticula affected the pT stage of the LAMNs. The immunohistochemistry information showed the same pattern with cytokeratin 7 (CK7) negative, cytokeratin 20 (CK20) positive and caudal type homeobox 2 (CDX-2) positive. No lymph node metastasis was found. The lack of treatment guidelines for LAMNs confined to the appendix and different acceptances of patients of preventive intervention led to varied clinical treatments. However, we found no short-term benefits of prophylactic extended resection or hyperthermic intraperitoneal chemotherapy.

Conclusion: LAMNs confined to the appendix are rare and must be differentiated from serrated lesions and diverticula. LAMNs with different pT stages have inert biological behavior. Determining the long-term effects of preventive treatment on survival and recurrence requires more data and a longer follow-up.