Introduction/Background*Endocrine therapy (ET) is a well-tolerated treatment strategy among women with low grade, hormone receptor positive advanced endometrioid endometrial cancer (EC).

Methodology In this retrospective cohort study, we identified patients with advanced endometrioid EC who were treated with ET between 2016-2018 by a medical oncologist at the Sunnybrook Odette Cancer Centre (Toronto, Canada). Descriptive analyses were performed. Median PFS from the time of starting ET and OS from diagnosis of advanced disease were assessed using Kaplan Meier methods. Predictors of PFS were evaluated using Cox regression models.

Result(s)*Twenty nine patients were included. Median age at diagnosis of advanced disease was 65.7 years. The majority of patients had grade 1 (55%) or grade 2 (29%) EC. Twenty three patients (79%) had ER and/or PR positive tumors (≥1% using immunohistochemistry); ER/PR status was negative in 1 case and unknown for 5 patients. Only 17% of patients received chemotherapy for advanced disease prior to starting ET. Letrozole (52%) and progestins (48%) were the most frequently used. Interestingly, the majority of patients (79%) received radiotherapy for oligoprogression while receiving ET.

Median PFS was 12.8 months. Median OS has not been reached, however, 73% of patients survived at least 4 years [95% Confidence Interval (CI) 56.4% to 95.5%]. Use of a progestin as first-line ET was associated with a longer PFS [Hazard Ratio (HR) 0.42; 95%CI 0.18-0.97, p=0.04], with a trend toward longer OS [HR 0.20; 95%CI 0.04-1.06, p=0.06]. Lack of oligoprogression requiring radiotherapy was associated with a longer PFS [HR 0.23; 95%CI 0.07-0.83, p=0.02], but not OS. Patient age, tumor grade, time to diagnosis of metastatic disease, stage at initial diagnosis, and use of chemotherapy prior to ET were not significantly associated with PFS or OS.

Conclusion*The clinical benefit of ET was greater in our cohort compared to prior published reports, possibly due to selection of patients with low grade and ER/PR positive tumors. The use of first-line progestins and lack of oligoprogression requiring radiotherapy were significantly associated with longer PFS in this small cohort.