Patterns of SATB2 and p16 Reactivity Aid Distinction of Atypical Polypoid Adenomyoma from Myoinvasive Endometrioid Carcinoma and Benign Adenomyomatous Polyp on Endometrial Sampling

AIMS Atypical polypoid adenomyoma (APAM) is an uncommon uterine lesion composed of complex endometrioid glands with frequent squamous morular metaplasia and fibromuscular stroma. On endometrial curettage, biopsy, or polypectomy specimens, the admixture of endometrioid glands and smooth muscle raises the differential diagnosis of myoinvasive endometrioid carcinoma. Reproductive age patients with APAM may opt for fertility preservation, whereas myoinvasive carcinoma is treated surgically. One previous study reported an incidental finding that the stroma of APAM, in contrast to other polypoid lesions, was positive for SATB2. APAM has also been reported to show increased stromal p16 staining. We aimed to assess whether SATB2 and p16 are useful stains for distinction of APAM from myoinvasive carcinoma and benign adenomyomatous polyps. METHODS AND RESULTS Cases of "atypical polypoid adenomyoma" (n=32), "adenomyomatous polyp" (n=39), and "myoinvasive endometrioid carcinoma" (n=30) were identified. Morphologic features were assessed, along with the intensity and extent of SATB2 and p16 expression in the stromal component of each lesion. SATB2 expression was seen in the stromal component of 30/32 (94%) APAM, compared to 0/39 (0%) benign adenomyomatous polyps and 5/30 (17%) myoinvasive endometrioid carcinomas. Stromal p16 expression was seen in 31/31 (100%) APAM, versus 20/39 (51%) benign adenomyomatous polyps and 12/30 (40%) myoinvasive endometrioid carcinomas. CONCLUSIONS Patchy to diffuse SATB2 reactivity and block-type p16 staining of fibromuscular stroma separating atypical endometrioid glands is more consistent with APAM than myoinvasive endometrioid carcinoma. These stains are potentially useful adjuncts to careful morphologic evaluation of endometrial biopsies/curettings.