Metformin for Chemoprevention of Lung Cancer in Overweight or Obese Individuals at High Risk for Lung Cancer

Inclusion Criteria:

Former smokers (male and female) with a >= 20 pack year smoking history
Quit smoking >= 12 months prior to enrollment
Prostate, Lung, Colorectal and Ovarian Cancer Screening Trial (PLCOm2012) Lung Cancer Risk Prediction Score > 1.34%

Overweight

Body mass index (BMI) > 25 and

Waist circumference

Female > 88 cm (35")
Male > 102 cm (40")
Age greater than 30 years. Participants younger than 30 years are unlikely to accrue enough smoking exposure followed by enough time after quitting (>12 months) to qualify
Eastern Cooperative Oncology Group (ECOG) performance status =< 2
Leukocytes >= 3,000/microliter
Absolute neutrophil count (ANC) >= 1,000/microliter
Platelets >= 100,000/microliter
Total bilirubin =< 1.5 x institutional upper limit of normal (IULN)
Aspartate aminotransferase (AST) (serum glutamic-oxaloacetic transaminase [SGOT])/alanine aminotransferase (ALT) (serum glutamate pyruvate transaminase [SGPT]) =< 3.0 x IULN
Estimated glomerular filtration rate (eGFR) > 45 ml/min/1.73 m^2 (eGFR will be calculated using the equation Chronic Kidney Disease Epidemiology Collaboration [CKD-EPI] creatinine)
Patients with a history of hepatitis C virus (HCV) infection must have been treated and cured
Patients on chronic suppressive antiviral therapy for herpes simplex virus (HSV) are eligible
The effects of metformin ER on the developing human fetus at the recommended therapeutic dose are unknown. For this reason, women of child-bearing potential and men must agree to use adequate contraception (hormonal or barrier method of birth control; abstinence) prior to study entry and for the duration of study participation. Should a woman become pregnant or suspect she is pregnant while participating in this study, she should inform her study physician immediately
Ability to understand and the willingness to sign a written informed consent document

Exclusion Criteria:

Current or previous diagnosis of diabetes mellitus (type I or type II diabetes)
Use of metformin within the past 2 years
Use of GLP-1 agonists within 6 weeks prior to enrollment
Glycosylated hemoglobin A1C (HbA1c) > 8%
History of allergic reactions attributed to compounds of similar chemical or biologic composition to metformin ER
Participants currently using immunosuppressive medication, including systemic steroids (not inhalational) and episodic use of inhaled steroids are excluded from this trial due to the potential impact of these treatments on the primary trial endpoint
Participants receiving any other investigational agents

History of chronic alcohol use or abuse defined by any one of the following:

Average consumption of 3 or more alcohol containing beverages daily in the past 12 months
Consumption of 7 or more alcoholic beverages within a 24 hour period in the past 12 months
Acute or chronic liver disease, evidence of hepatitis (infectious or autoimmune), cirrhosis or portal hypertension
History of or current condition predisposing to increased risk for lactic acidosis such as: severe congestive heart failure (New York Heart Association [NYHA] class III or IV), metabolic acidosis, severe liver disease, or renal failure
Uncontrolled intercurrent illness or psychiatric illness/social situations that would or limit compliance with study requirements
Pregnant women are excluded from this study. Metformin ER is a class B agent that was not teratogenic in rats and rabbits at doses representing 3 and 6 times the maximum recommended human daily dose of 2000 mg; however, animal reproduction studies are not always predictive of human response. Because there is an unknown but potential risk for adverse events (AEs) in nursing infants secondary to treatment of the mother with metformin ER, breastfeeding should be discontinued if the mother is treated with metformin ER

Biopsy with invasive carcinoma of the lung or carcinoma in situ

Participants with prior stage 1 non-small cell lung cancer (NSCLC) diagnosis are allowed to participate, as long as there has been 12 months since the completion of cancer treatment prior to enrollment with no evidence of recurrence or second primary cancer