Clinicopathological and immunohistochemical features of uterine adenomyomatous polyps.

Adenomyomatous polyps (APs) of the uterus (also termed polypoid adenomyomas and pedunculated adenomyomas) are exophytic proliferations composed of myomatous stroma admixed with endometrial glands. APs can be diagnostically challenging, mimicking polypoid neoplasms such as atypical polypoid adenomyoma and adenosarcoma. The purpose of this study was to describe the clinicopathological, morphologic, and molecular features of APs, as well as to raise awareness of this entity as a potential source of diagnostic confusion. We identified APs diagnosed at Brigham and Women's Hospital from 2000 to 2015. We reviewed histologic slides and obtained archival tissue for immunohistochemical and molecular studies. APs seen in consultation were associated with a broad differential, including adenosarcoma, atypical polypoid adenomyoma, and endometrial neoplasia. We performed a histologic review of 84 APs diagnosed at our institution and identified 2 distinct morphologic types of APs, which we have termed type 1 (with vaguely fascicular myomatous stroma intimately admixed with glands) and type 2 (containing a well-defined stalk of smooth muscle entrapping glands). Most APs exhibited CD10-positive (100%; 72/72) and desmin-positive (97%; 70/72) stroma. Diffuse caldesmon positivity was present in 97% (28/29) of type 2 polyps compared with 8% (3/39) of type 1 APs. APs did not harbor mutations in exon 2 of MED12. APs are not uncommon in routine practice and may be misinterpreted as more worrisome lesions. We identified 2 types of APs with distinct morphology and immunophenotype. The absence of MED12 exon 2 mutations suggests that the pathogenesis of APs is separate from uterine leiomyomas.