Introduction CDK 4/6 inhibitors (CDK4/6i) with endocrine therapy (ET) has promising phase II results in estrogen receptor (ER)+ recurrent/advanced endometrial cancer (EC). The purpose of our study is to evaluate characteristics and clinical outcomes of patients with ER+EC who have received a CDK4/6i+ET at our institution.

Methods This is a multi-center institution retrospective chart review, which included patients diagnosed with endometrial cancer and treated with CDK4/6i+ET between 2016- March 2023 for ≥1 month in duration. Outcomes evaluated included time to treatment failure (TTF) and progression free survival (PFS).

Results Thirteen patients were identified, with an average age of diagnosis at 61 years (IQR: 50–68). The most common histopathologic diagnosis was endometrioid (n=8, 61.5%), followed by endometrial stromal sarcoma (ESS) (n=4, 30.8%). The median follow-up after CDK4/6i was 8.6 months (IQR 4.7–17.5). The median number of treatments since recurrence was 2, including 9 with prior ET. The TTF in the endometrioid group was 5.1 months (95% CI 3.8-NR), where PFS was not reached (NR) (95% CI 5.4-NR). The TTF and PFS in the ESS group was the same at 9.8 months (95% CI 7.9-NR). Four patients were still on treatment upon study completion, five patients discontinued due to disease progression, and four discontinued because of toxicity.

Conclusion/Implications Patients with ER+EC have reasonable responses to CDK4/6i+ET with the majority of patients with endometrioid histology discontinuing due to toxicity rather than progression. This data supports the findings from the previously published clinical trials that CDK4/6i+ET should be considered as a treatment option in recurrent ER+EC.