The anti-diabetic drug phenformin may prompt stronger cancer-fighting activities than its sister compound metformin, a finding that could have major implications for current and future clinical trials investigating both agents for their anti-cancer potential, according to researchers at Massachusetts General Hospital (MGH). In a review article in Trends in Cancer, the team presented evidence that immunotherapies such as immune checkpoint inhibitors (which enable T cells to attack and kill cancer cells) in combination with phenformin may also be a promising way to repurpose this diabetic drug as an anti-cancer agent.