Abstract 1124: Discordance between gross and histologic findings in progestin-treated endometrial neoplasia

Introduction: Hysterectomy with or without lymphadenectomy remains the first line of therapy for endometrial cancer (EC). Rising levels of obesity coupled with a trend toward delayed childbearing has led to an increasing population of young women with EC who are poor surgical candidates due to obesity or desire fertility preservation. Accordingly, progestin-based therapy is gaining momentum nationally. Nevertheless, some patients ultimately undergo surgery. Progestin-treated EC can undergo marked stromal decidualization. We hypothesized that this treatment effect may create the false impression of a large residual endometrial tumor burden at the time of gross intra-operative tumor assessment (ITA). As ITA can guide the decision to pursue lymphadenectomy and/or oophorectomy, particularly in community hospitals, familiarity with the gross findings in this setting is essential in order to inform optimal patient management. Methods: 12 hysterectomy specimens with reported progestin-related changes following a diagnosis of atypical hyperplasia or FIGO grade 1-2 EC were identified over a 10-year period. Patient age, duration of progestin therapy, and gross tumor size were recorded. Tumors were histologically assessed for the extent to which decidualized stroma comprised grossly identified lesions and were categorized as having minimal ( 50%) stromal decidualization. Results: Patients9 ages ranged from 28-59 years of age (median 41.5 years). 8 were premenopausal and 4 were postmenopausal. Indications for progestin therapy included fertility preservation and a bridge to surgery in patients not desiring fertility. Duration of therapy ranged from 17-332 days (median 80 days). Grossly visible lesions were described in all cases with a median size of 4.1 cm (range 1-8.2 cm). The decidual component was minimal in 3 cases, intermediate in 4 cases, and extensive in 5 cases. 2 cases with grossly visible lesions (2.2 & 7 cm in size) had only focal residual hyperplasia. Extensive decidualization was more common in premenopausal (median 65%, range 10-90%) than in postmenopausal women (median 18%, range 10-40%; p=0.06), irrespective of time on progestin therapy (102.5 vs. 80 days, p=0.87). Conclusions: Large mass lesions following progestin therapy may histologically consist primarily of decidualized stroma with little to no residual neoplastic disease. In these cases, the perceived tumor size does not reflect the actual residual tumor burden; this effect appears to be more pronounced in pre-menopausal patients. In the setting of intraoperative decision-making based on gross tumor assessment, this discrepancy between gross and histologic findings may lead to unnecessary lymphadenectomy and its associated morbidity. Citation Format: Yang Hu, Ahmed N. Al-Niaimi, Alain P. Cagaanan, Paul Weisman, Stephanie M. McGregor. Discordance between gross and histologic findings in progestin-treated endometrial neoplasia [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1124.