The purpose of this trial was to test if enzalutamide + metformin in patients with mCRPC progressing on ADT is more effective compared to enzalutamide alone.
SAKK 08/14 is a prospective multicenter, 1:1 randomized, open-label, phase 2 trial. Patients with mCRPC progressing on ADT and no prior or current therapy for diabetes mellitus were eligible. Patients received enzalutamide 160 mg OD alone or in combination with metformin 850 mg BID:
The primary endpoint of the trial was disease control rate at 15 months, defined as complete response or partial response achieved for at least one assessment within the first 15 months (+/- 6 weeks) of initial treatment, or stable disease maintained during treatment for at least 15 months (+/ 6 weeks) after treatment start. Secondary endpoints include OS, event-free survival, time to PSA progression, adverse events and quality of life. In order to show superiority for enzalutamide + metformin a total of 168 evaluable patients were needed to detect a 20% difference in disease control rate at 15 months (type I error 10%, power 80%).
There were 166 patients accrued from June 2016 – February 2021 in 16 Swiss centers, with a median follow-up of 44 months (95% CI 39.0-48.7). Baseline characteristics were as follows:
The primary endpoint was not met: disease control rate at 15 months was 52.4% for enzalutamide + metformin (90% CI 42.9% - 61.8%) and 56.1% for enzalutamide (90% CI 46.4% - 65.4%), respectively (p = 0.644). There was a trend towards improved median event-free survival for enzalutamide + metformin vs enzalutamide (19.3 (95% CI 12.5, 28.1) vs. 15.1 (95% CI 12.1, 21.4) months; HR 0.87, 95% CI 0.60-1.26; p = 0.47), and median time to PSA progression (15.8 (95% CI 11.4, 20.6) vs. 11.0 (95% CI 9.4, 13.2) months; HR 0.71, 95% CI 0.49-1.04; p = 0.074):
and median time to pain progression (41.7 (95% CI 16.9, NA) vs. 20.3 (95% CI 14.2, 58.4) months, HR 0.84, 95% CI 0.51 – 1.37; p = 0.47):
In a subgroup analysis, there was a signal for improved event-free survival and time to PSA progression among overweight + obese men who received enzalutamide + metformin:
The median OS was similar in both arms (38.7 (95% CI 25.9, 50.0) and 40.9 (95% CI 28.3, 51.7) months; HR 1.13 (95% CI 0.74, 1.71); p = 0.575). Treatment-related adverse events were comparable between the two arms.
Dr. Rothermundt concluded his presentation discussing SAKK 08/14 – IMPROVE, a randomized, open-label, phase II trial assessing metformin in patients with mCRPC in combination with enzalutamide versus enzalutamide alone with the following take-home messages:
- This is the first randomized study to investigate enzalutamide + metformin in mCRPC and it was negative for the primary endpoint of disease control rate at 15 months
- However, metformin may have a modest effect on PSA dynamics and symptom control
- Unplanned subgroup analyses suggest better outcomes for overweight and obese patients compared to normal-weight patients
- Larger studies are needed for confirmation
Presented by: Christian A. Rothermundt, Department of Haematology And Oncology, Kantonsspital St. Gallen, St. Gallen, Switzerland
Written by: Zachary Klaassen, MD, MSc – Urologic Oncologist, Assistant Professor of Urology, Georgia Cancer Center, Augusta University/Medical College of Georgia, @zklaassen_md on Twitter during the 2022 European Society of Medical Oncology (ESMO) Annual Hybrid Meeting, Paris, FR, Fri, Sept 9 – Tues, Sept 13, 2022.