It was set to be the largest breast cancer trial of its kind. Medical oncologist, clinican scientist and former Director of the Marvelle Koffler Breast Centre, Dr. Pamela Goodwin had nearly everything she needed — interested patients, millions in funding, support from the Canadian Cancer Trials Group — except for the drug at the centre of her trial.

Metformin, a common and relatively inexpensive diabetes drug, was theorized to hold enormous promise in treating breast cancer. But without access to the medication, Dr. Goodwin and her trial were stuck.

“Despite securing $40 million in funding needed for the trial, we struggled to find a pharmaceutical company that would provide the generic version of metformin and, more importantly, placebo for use in the study,” she said.

Metformin belongs to a class of drugs called biguanides, which are used to treat high blood sugar or diabetes. It was theorized that the drug might slow breast cancer growth by improving patient metabolism, notably insulin levels, leading to reduced growth of cancer cells, or that it might impact cancer cells directly.

With nowhere else to turn, Dr. Goodwin reached out to Toronto philanthropist and long-time Sinai Health supporter Murray Koffler. The former pharmacist and founder of Shoppers Drug Mart immediately offered to help.

“He said ‘Give me five minutes,'" Dr. Goodwin recalls. “Sure enough, within a matter of minutes, he connected with the late Apotex founder Barry Sherman, who instantly agreed to provide the generic version of metformin and an identical placebo for the trial. It was remarkable.”

Almost 15 years later, Dr. Goodwin presented her findings to some of the biggest minds in breast cancer research at the 2021 San Antonio Breast Cancer Symposium. Her study tracked more than 3,600 breast cancer patients from across Canada, the U.S., Switzerland and the U.K. The results have yet to be peer reviewed.

Dr. Goodwin ultimately found that the addition of metformin to standard breast cancer treatments does not prevent or stop the spread of the most common forms of the disease, however, for individuals with a less common but aggressive form of the disease, called HER2-positive breast cancer, there was evidence that use of metformin for five years might lead to a significant reduction in deaths.

“The results tell us that metformin is not effective against the most common types of breast cancer and any off-label use of this drug for the treatment of these common types of breast cancer should be stopped,” Dr. Goodwin said. “The results in HER2-positive breast cancer are promising and will lead to more research.”

This research was funded by the Canadian Cancer Society, the National Cancer Institute (U.S.), the Canadian Breast Cancer Foundation, the Breast Cancer Research Foundation, Cancer Research UK, Hold'em for Life Charity Challenge and Apotex (Canada).

ILLUSTRATION BY SALINI PERERA