Atypical polypoid adenomyoma of the uterus: A reappraisal of the clinicopathological and immunohistochemical features.

Atypical polypoid adenomyoma (APAM) is an uncommon uterine mixed epithelial and mesenchymal tumor. The discrimination from endometrial carcinoma remains to be clarified. In this study, we compared the clinicopathological and immunohistochemical features between 36 APAMs and 48 endometrial carcinomas. APAM with a highly complex structure (n = 13) coexisted with atypical hyperplasia (n = 5) and endometrial carcinoma (n = 1). Two patients had endometrial carcinomas at 1 and 102 months. Four patients recurred at 1-57 months but none died of disease. The fibromuscular stroma demonstrated 3 uncharacterized features: a broad bundle (10/36), a lobular structure separated by the stromal branches (26/36), and the extension of fibromuscular stroma underneath the surface epithelium (31/36). However, these features were not seen in endometrial carcinomas except the vaguely lobular pattern. Both APAM and endometrial carcinoma showed a similar immunostaining pattern except high Ki67 index in endometrial carcinomas (p < 0.05). Our study suggests that the distinct features of the fibromuscular stroma can aid in the differential diagnosis between APAM and endometrial carcinoma.