Objectives Adenomyosis (AM) is very often diagnosed in histology slides of endometrioid endometrial adenocarcinoma (EEAC). The combination of EEAC and AM has not been investigated sufficiently. The aim of this study is to evaluate the combination of AM and EEAC in morphological and morphometrical terms and to reflect a possible role of AM in the pathogenesis of EEAC.

Methods A retrospective review of an institutional pathology archive over a five-year-period was performed to identify cases of combined EEAC and AM. 79 cases were identified. Histological slides exhibiting the combination of AM and EAC were digitalised using Aperio Slide scanner and evaluated by using Aperio Morphometry tools. Morphological results were correlated with tumour type, tumour grade and staging and compared with routine AM (RAM) cases. In a next step all histological slides were immunohistochemical examined by different antibodies.

Results The mean distance AM – EEAC was 0,67 ± 0,75 mm, the mean AM gland size was 0,22 ± 0,10 mm, while the mean RAM gland size was 2,31mm. All EAC cases were type 1 EEAC. The majority of AM-EEAC cases were classified as stage pT1a tumours and graded as G1. Immunohistochemical we were able to distinguish betweena p16 positive and p16 negative group.

Conclusions AM in combination with EEAC exhibits a special morphology with small AM glands near the EEAC. Our hypothesis is that Adenomyosis could be involved in the pathogenesis of endometrial cancer or a random incidental finding. Adenomyosis in the p16 negative group could play a rule in carcinogenesis.