CCTG MA32 trial was published recently in the Journal of the American Medical Association

The findings of the CCTG MA32 trial were published recently in the Journal of the American Medical Association. According to the study results, 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 landmark trial, led by Dr. Pamela Goodwin at Sinai Health and run by the Canadian Cancer Trials Group (CCTG) under the umbrella of the Breast International Group (BIG) network, is the largest of its kind to date, tracking more than 3,600 breast cancer patients from across Canada, the U.S., Switzerland and the U.K.

“The results tell us that metformin is not effective against the most common types of breast cancer and any off-label use for this drug for the treatment of these common types of breast cancer should be stopped,” said Dr. Goodwin, a medical oncologist at Sinai Health and a clinician scientist at the Lunenfeld-Tanenbaum Research Institute in Toronto.

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 CCTG MA32 trial illustrates the importance of international academic group collaboration to test new treatment approaches with a goal to advance clinical care,” said CCTG Senior Investigator Dr. Wendy Parulekar. “The results of all Phase III trials inform current treatment standards and generate hypotheses to be tested in future studies. CCTG is grateful to the all the patients and families, health care teams, granting agencies and collaborators who enabled the successful conduct of the trial.”

Goodwin PJ, Chen BE, Gelmon KA, Whelan TJ, Ennis M, Lemieux J, Ligibel JA, Hershman DL, Mayer IA, Hobday TJ, Bliss JM, Rastogi P, Rabaglio-Poretti M, Mukherjee SD, Mackey JR, Abramson VG, Oja C, Wesolowski R, Thompson AM, Rea DW, Stos PM, Shepherd LE, Stambolic V, Parulekar WR. Effect of Metformin vs Placebo on Invasive DiseaseFree Survival in Patients With Breast Cancer: The MA.32 Randomized Clinical Trial. J Am Med Assoc 327: 1963-73, 2022.