Common diabetes drug effective against early-stage breast cancer?

According to new findings, a widely used and inexpensive Type 2 diabetes drug, once hoped to hold enormous promise in treating breast cancer, does not prevent or stop the spread of the most common forms of the disease.

The randomized, double-blind trial enrolled patients who were treated with two pills a day of either placebo or the diabetes drug metformin. Overall, researchers found the addition of metformin to standard breast cancer treatments did not improve outcomes in the two most common types of breast cancer, hormone receptor-positive or negative. The findings were published in the Journal of the American Medical Association.

While metformin was found not to be effective in treating the most common forms of breast cancer, the trial found a potentially important result for individuals with a less common but aggressive form of the disease, called HER2-positive breast cancer. For the subtype of breast cancer, researchers found there was evidence that use of metformin for five years might lead to a reduction in deaths. HER2-positive cancer makes up about 20 per cent of all breast cancers. 

Metformin is not beneficial for use in most common breast cancers, but in the cases of HER2-positive breast cancer, these findings suggest it may be beneficial.