Abstract A021: Pilot study of daily exemestane in patients with Endometrial Intraepithelial Neoplasia (EIN) or grade 1 endometrial cancer

Abstract

Abstract Introduction: The purpose of this study is to evaluate exemestane, an aromatase inhibitor, as a potential agent for the chemoprevention of endometrial cancer. Experimental procedures: This is a multi-center, phase IIA, single arm ‘window of opportunity’ pilot study of 25 mg per day of exemestane for 21-42 days in postmenopausal patients undergoing hysterectomy for endometrial intraepithelial neoplasia (EIN) or low-grade endometrial cancer. The primary objective is to determine if there is a decrease in proliferation index, measured by percent Ki-67 expression in endometrial tissue, from pre-treatment to post-exposure. Results of Ki-67 are compared with a historic control cohort of tumors from patients matched by preoperative histologic diagnosis, age, BMI category. Specimens from the historic control cohort included a preoperative endometrial biopsy as well as a surgical specimen, separated in time by less than 42 days. Secondary outcomes include comparison of Ki67 to historic controls, circulating serum estradiol and progesterone levels, pathologic response, tissue biomarkers, safety and adverse effects. Summary of Data: Forty patients accrued to the study between January of 2018 and March of 2021. The mean age was 63 (range 52-75). Thirty-nine patients (97.5%) self identifiedself-identified as white; 1 patient (2.5%) identified as Asian. The mean BMI was 40.3 (SD 9.75, range 22.8-60.5). Preoperative diagnoses included EIN, grade 1 endometrial adenocarcinoma, and grade 2 endometrial adenocarcinoma in 11 (27.5%), 26 (65%), and 3 (7.5%) patients respectively. Thirty-nine patients (97.5%) were compliant with exemestane dosing. All patients completed the study and no patients discontinued or interrupted therapy due to treatment related adverse events. Thirty-eight patients had evaluable specimens for both pre and post-treatment Ki-67 analysis. Median Ki-67 score decreased from 40.7% [IQR (33.9%, 50.3] at baseline to 18.1% [IQR (8.8%, 31.8%)]. This represents a median absolute change from baseline of -20.4% [IQR (-29.9, -6.7), p<0.001]. In total, percentage of Ki-67 in tumor cells declined in 31 patients and increased in 7 patients. In the historic control cohort, patients also had a decrease in Ki-67 score with a median absolute change from baseline of -6.7% [IQR (-12.7%, -1.3%), p<0.001]. However, the decrease in Ki-67 was greater in the study patients than the matched historic controls, with a median difference between the groups of -13.4% [IQR= (-23.3%, 6.9%), p=0.0095]. Serum estradiol levels did not change significantly between baseline and post-treatment (p=0.16). There was a small but significant increase from baseline to post-treatment in serum progesterone (0.14 ng/mL vs 0.37 ng/mL, p<0.001). Conclusion: In this pilot window of opportunity study, exemestane demonstrates anti-proliferative effects in endometrial intraepithelial neoplasia and low-grade endometrial cancer. This agent warrants further evaluation for the chemoprevention of endometrial cancer. Citation Format: Britt K. Erickson, Lisa Barrioullet, Rebecca C. Arend, Dina El-Rayes, Mahmoud Khalifa, Amy Skubitz, Kristin Boylan, Andrew Nelson, Bharat Thyagarajan, Thomas Havighurst, Richard Chappell, Eileen Dimond, Katina Deshong, Goli Samimi, Eva Szabo, Howard Bailey. Pilot study of daily exemestane in patients with Endometrial Intraepithelial Neoplasia (EIN) or grade 1 endometrial cancer [abstract]. In: Proceedings of the AACR Special Conference on Endometrial Cancer: Transforming Care through Science; 2023 Nov 16-18; Boston, Massachusetts. Philadelphia (PA): AACR; Clin Cancer Res 2024;30(5_Suppl):Abstract nr A021.