Metformin is thought to activate AMP-activated protein kinase (AMPK), a major sensor of cellular energy levels and a key enzyme limiting cellular growth during times of cellular stress. Once activated, this enzyme restricts anabolic processes such as protein, cholesterol and fatty acid synthesis and inhibits mTOR, a protein kinase responsible for unregulated growth. MTOR is upregulated in a variety of tumors, including NSCLC providing rationale to take advantage of this pathway with metformin.