Atypical mucinous glandular proliferations in endometrial samplings: follow-up and other clinicopathological findings in 41 cases.

The 2014 World Health Organization classification calls for endometrial mucinous proliferations that display "confluent or cribriform architecture with even minimal atypia" in sampling specimens to be classified as carcinoma, and others whose features are not diagnostic of carcinoma to be categorized as atypical mucinous glandular proliferations (AMGPs). Herein, we evaluate follow-up findings in 41 cases that were classified as AMGP from our files. The average patient age was 46years (range, 37-59 years). Postbiopsy follow-up duration ranged from 15 to 109weeks (mean, 40 weeks). There was no follow-up resection in 12 patients (9 with repeat biopsies, all 9 with no clinical evidence of disease, mean follow-up of 43weeks), and 29 patients underwent a hysterectomy an average of 2.4months after the index biopsy. The distribution of pathologic findings in the uteri was as follows: no residual AMGP or carcinoma (5/29; 17%), AMGP (11/29; 38%), and adenocarcinoma (13/29; 45%). All adenocarcinomas were grade I and stage I, and histotypes were endometrioid (n=8), mucinous (n=3), and endometrioid with mucinous differentiation (n=2). Only 3 (23%) carcinomas were myoinvasive, of which 1 case, a mucinous carcinoma with a 40% endometrioid component, showed greater than 50% myometrial invasion. None of a wide array of morphologic features was significantly associated with a hysterectomy diagnosis of carcinoma (versus AMGP) on univariate analyses. In conclusion, our cohort of AMGP represents a biologically variable spectrum of lesions that includes mucinous hyperplastic proliferations as well as endometrioid and mucinous adenocarcinomas that are occasionally myoinvasive. Morphologic features that optimally stratified AMGP cases into clinically relevant subgroups were not identified.