A Randomized Placebo-Controlled Phase 2 Study of Metformin for the Prevention of Progression of Monoclonal Gammopathy of Undetermined Significance and Low Risk Smoldering Multiple Myeloma

Background: Multiple Myeloma (MM) is thought to evolve from the precursor conditions monoclonal gammopathy of undetermined significance (MGUS) and smoldering MM (SMM), which are common premalignant disorders that progress to overt MM in a subset of individuals for reasons that are poorly understood. Despite increasing interest in preventing disease progression in this patient population, the standard of care still consists of close surveillance until progression to MM; however, once MM develops it cannot be cured. Therefore, the identification of prevention and interception strategies for patients with MGUS and SMM is of considerable importance.

A promising pharmacologic intervention to reduce the risk of progression of MGUS/SMM to MM is metformin, a drug commonly used to treat type 2 diabetes but that is also considered safe for use in non-diabetic populations. In vivo and in vitro studies have revealed that metformin has direct antitumor effects across a variety of cancers including MM, and recent epidemiological data suggests it may reduce the risk of MM in diabetic patients with MGUS. Here, we describe the first randomized controlled trial testing the efficacy of metformin in reducing clinical signs of disease progression in patients with MGUS and SMM (NCT04850846).

Study Design and Methods: This is a phase II single center, randomized controlled trial of metformin vs. placebo in patients with high-risk MGUS and low-risk SMM. The primary objective of the study is to determine whether metformin can reduce or stabilize serum monoclonal (M-)protein concentrations from baseline to 6-months. Exploratory objectives include mass spectrometry quantification of M-protein, examination of molecular evolution of tumor cells in response to metformin, as well as changes in other clinical laboratory parameters in response to metformin.

To be eligible, patients must have high-risk MGUS or low-risk SMM. High-risk MGUS is defined as bone marrow plasma cell concentration <10% with one or more of the following higher-risk features: serum M-protein level ≥1.5 g/dL to <3 g/dL or abnormal free light-chain (FLC) ratio (<0.26 or>1.65); a forthcoming amendment will include non-IgG subtype as an additional high-risk feature. Low-risk SMM is defined as bone marrow plasma cells ≥10%with the absence of any features of high-risk SMM.

Metformin and its corresponding placebo are the pharmacological treatments. The metformin dose is 1500 milligrams/day, provided in 500 milligram pills. To minimize gastrointestinal symptoms, metformin is started at a low dose of 500 milligram (1 pill) per day and participants gradually increase the dosage over the course of the first month of treatment until the full 1500 milligram (3 pill) per day regimen is achieved. The study treatment period is 6 months, with primary outcomes assessed at the end of the 6-month treatment period.

Conclusions and Future Directions: While the cornerstone of clinical management in MGUS and SMM is to delay therapy until progression to symptomatic MM, patients and oncologists continually seek new ways to prevent end organ damage and incurable malignancy. This trial is positioned to provide preliminary but robust mechanistic data to support the development of novel prevention strategies for MGUS and SMM patients.