Stromal p16 and SATB2 Expression Does Not Distinguish Atypical Polypoid Adenomyoma (APA) From its Benign Mimics

Atypical polypoid adenomyoma (APA) is a polypoid biphasic lesion of low malignant potential that arises in the lower uterine segment and uterine corpus. The diagnosis of APA is often challenging on biopsy and curettage specimens, and both benign and malignant processes need to be considered in the differential. Stromal expression of p16 and SATB2 have recently been shown to distinguish APA from myoinvasive endometrioid carcinoma. The authors hypothesized that p16 and SATB2 immunohistochemistry could also aid in the distinction of APA from benign adenomyomatous polyp and endometrioid adenomyoma. The study comprised 10 APAs, 7 adenomyomatous polyps, 11 endometrioid adenomyomas, and 10 myoinvasive endometrioid carcinomas. The majority of APAs showed moderate to strong, diffuse p16 and stromal expression. However, most adenomyomatous polyps and endometrioid adenomyomas also exhibited moderate to strong, focal to diffuse p16 stromal expression. SATB2 showed weak to moderate, focal to diffuse expression in the majority of APAs, adenomyomatous polyps and endometrioid adenomyomas. In contrast, p16 and SATB2 were negative to weak and focal in 90% of myoinvasive endometrioid carcinomas. Our findings demonstrate that p16 and SATB2 may be helpful in the differential diagnosis of myoinvasive endometrioid carcinoma and APA while not useful in separating APA from adenomyomatous polyp and endometrioid adenomyoma.