Metformin in Chemotherapy-naive Castration-resistant Prostate Cancer: A Multicenter Phase 2 Trial (SAKK 08/09)
Rothermundt C1, Hayoz S2, Templeton AJ3, Winterhalder R4, Strebel RT5, Bärtschi D2, Pollak M6, Lui L6, Endt K7, Schiess R7, Rüschoff JH8, Cathomas R5, Gillessen S9. Eur Urol. 2014 Jan 4. pii: S0302-2838(13)01482-6. doi: 10.1016/j.eururo.2013.12.057. [Epub ahead of print]

Author information

1Cantonal Hospital St. Gallen, St. Gallen, Switzerland. Electronic address: christian.rothermundt@kssg.ch. 2SAKK Coordinating Center Bern, Bern, Switzerland. 3Cantonal Hospital St. Gallen, St. Gallen, Switzerland; SAKK Coordinating Center Bern, Bern, Switzerland. 4Cantonal Hospital Lucerne, Lucerne, Switzerland. 5Cantonal Hospital Chur, Chur, Switzerland. 6Lady Davis Institute for Medical Research Jewish General Hospital Montréal, Montréal, Canada. 7ProteoMediX, Schlieren, Switzerland. 8Institute of Surgical Pathology University Hospital Zurich, Zurich, Switzerland. 9Cantonal Hospital St. Gallen, St. Gallen, Switzerland.

Abstract

BACKGROUND: There is evidence linking metformin to improved prostate cancer (PCa)-related outcomes.

OBJECTIVE: To evaluate treatment with metformin in patients with castration-resistant PCa (CRPC) and the effect of the treatment on progression-free survival (PFS) and PSA doubling time (PSA DT).

DESIGN, SETTING, AND PARTICIPANTS: Forty-four men with progressive metastatic CRPC from 10 Swiss centers were included in this single-arm phase 2 trial between December 2010 and December 2011.

INTERVENTION: Patients received metformin 1000mg twice daily until disease progression.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS: The primary end point was the absence of disease progression at 12 wk. Simon two-stage optimal design was applied. With a 5% significance level and 90% power, 44 patients were required to test PFS at 12 wk ≤15% (H0) compared with ≥35% (H1).

RESULTS AND LIMITATIONS: Thirty-six percent of patients were progression-free at 12 wk, 9.1% were progression-free at 24 wk, and in two patients a confirmed ≥50% prostate-specific antigen (PSA) decline was demonstrated. In 23 patients (52.3%) we observed a prolongation of PSA DT after starting metformin. The homeostatic model assessment index fell by 26% from baseline to 12 wk, indicating an improvement in insulin sensitivity. There was a significant change in insulin-like growth factor-1 and insulin-like growth factor binding protein 3 from baseline to 12 wk. Sample size and lack of a control arm are the limitations of this trial; analyses are therefore exploratory.

CONCLUSIONS: Treatment with metformin is safe in nondiabetic patients, and it yields objective PSA responses and may induce disease stabilization. The activity of metformin in PCa, along with its low cost, favorable toxicity profile, and positive effect on metabolic parameters, suggests that further investigation of metformin as therapy for patients with PCa is of interest.

PATIENT SUMMARY: In this trial we assessed the use of the diabetes mellitus drug metformin in patients with advanced prostate cancer. We found disease stabilization and prolongation of prostate-specific antigen doubling time in some patients as well as effects on metabolic parameters.

TRIAL REGISTRATION: This study is registered with ClinicalTrials.gov with the identifier NCT01243385.

PREVIOUS PRESENTATION: The study was presented at ESMO 2012 (abstract 1460).