Background: * Li Fraumeni Syndrome (LFS) is a highly penetrant, autosomal dominant cancer predisposition disorder. Four main cancer types including sarcoma, adrenocortical carcinoma, breast cancer, and malignant brain tumors commonly characterize LFS but the syndrome can include other cancers. * Metformin is an oral biguanide drug that is approved by the FDA for the treatment of type II diabetes. Metformin has been associated with reduced cancer risk in several epidemiologic studies and reduced cancer mortality in patients with type 2 diabetes. * Metformin decreases circulating insulin and IGF1, and promotes glucose uptake in skeletal muscle and inhibits gluconeogenesis in the liver. Elevations in circulating insulin and IGF1 levels have been associated with increased cancer risk. * Preclinical research in animal models shows that metformin may be more toxic in cancer cells that have lost p53 function. * Lifetime risk of cancer in LFS patients with germline TP53 mutations is estimated to be up to 70% by age 60, with women having excess lifetime cancer risk (up to 100%) compared to men (up to 80%). There are currently no approved chemopreventive agents for patients with LFS. * Metformin has been shown to be safe and tolerable in diabetic and non-diabetics, and may be an ideal candidate for chemoprevention of cancer in this population. Objectives: * Determine the tolerability of oral daily metformin in patients with LFS caused by germline TP53 mutations. * Determine if 8 weeks of daily metformin administration has any effect on circulating IGF-1, insulin, and IGFBP3 Eligibility: * Must have a germline TP53 mutation and provide documentation of testing. * Must have adequate organ function. * Age greater than or equal to 18 years. Design: * This is a pilot study to assess the tolerability of daily oral metformin administration in patients with LFS caused by germline TP53 mutations and to study the effect of metformin on biomarker levels in these subjects. * In the absence of intolerable toxicity, a minimum of 22 patients will take metformin by mouth for a total of 14 weeks and then discontinue metformin for 6 weeks. The total time on study will be 20 weeks. * Patients will be assessed for biomarker levels (IGF-1, insulin, IGFBP3) by blood sample at baseline, and weeks 0 and 8.
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Determine the tolerability of metformin in patients with LFS caused by germline TP53 mutations
Timeframe: 2 years
Determine if 8 weeks of daily metformin administration has any effect on circulating IGF-1, insulin, and IGFBP3
Timeframe: 2 years