Hello! I am still traveling on a reporting trip, so this will be a brief newsletter. Today, we’re going to talk a little bit about a JAMA Network Open paper that seems to be making the rounds. Here investigators published observational data that seem to suggest GLP-1 inhibitors improve survival of breast cancer at first glance. At a deeper look, though, the result that GLP-1 inhibitor use reduces mortality by 91% in patients who also have diabetes seems unrealistic.

There are a couple of big reasons why this number is likely overstating the benefit of GLP-1 inhibitors in breast cancer, one being that patients with more aggressive cancer didn’t get a chance to fill prescriptions and be classified as a GLP-1 user. So, there’s an immortal time bias. The second part is the benefit basically goes away when adjusting for SGLT2 inhibitors.

There are reasonable hypotheses to why GLP-1 use could improve breast cancer outcomes, and it’s interesting to see this paper raise the discussion. A more definitive answer will need more study.