Clinicopathological Characteristics of Low-Grade Appendiceal Mucinous Neoplasm

<b><i>Introduction:</i></b> Recently, “low-grade appendiceal mucinous neoplasms” (LAMNs) have been proposed as one subtype of appendiceal mucinous neoplasms, characterized by a villous or flat proliferation of mucinous epithelium with low-grade cytologic atypia. The aim of this study was to clarify the clinicopathological characteristics of LAMN. <b><i>Methods:</i></b> In this multi-institutional cohort study, we retrospectively analyzed the clinicopathological characteristics in appendiceal neoplasms patients who underwent treatment from 2000 to 2017. <b><i>Results:</i></b> In total, 922 patients were enrolled, with 279 (30.3%) cases of LAMN, and 93 (10.1%) cases of non-LAMN disease. In comparison with patients with non-LAMN disease, those with LAMN had significantly lower levels of CA19-9 (<i>p</i> = 0.045), a lower frequency of T4 tumors (<i>p</i> &#x3c; 0.0001), a lower frequency of lymph node metastasis (<i>p</i> &#x3c; 0.0001), and a lower frequency of distant metastasis (<i>p</i> &#x3c; 0.0001). Survival analysis revealed that patients with LAMN had a significantly better prognosis than did those with non-LAMN disease (<i>p</i> &#x3c; 0.001). Among the patients with distant metastasis, those with LAMN had a significantly better prognosis than did those with non-LAMN disease (<i>p</i> = 0.0020), but among the patients without distant metastasis, the difference between the 2 groups was not significant (<i>p</i> = 0.26). However, among patients who underwent complete resection, the difference in prognosis between the 2 groups was not significant (<i>p</i> = 0.10). <b><i>Conclusions:</i></b> A multicenter retrospective study revealed that the clinicopathological characteristics of LAMN was different from those of non-LAMN.