“We found that metformin alone reduces PSA levels in a significant number of patients, as well as modulating the immune system,” said Sylvester researcher Marijo Bilusic, M.D., Ph.D., a medical oncologist who specializes in genitourinary cancers and first author on the paper. “We don’t fully understand what’s driving these changes, but this is definitely something we need to study further.”
The research evolved from Dr. Bilusic’s experience with several prostate cancer patients who had experienced biochemical recurrence, which is generally an increase in PSA levels despite previous treatments. However, the PSA levels in these patients mysteriously dropped. A little sleuthing soon found the common thread: all the patients had type 2 diabetes and were taking metformin. This dovetailed with epidemiological studies showing people who take metformin have lower cancer rates and cancer mortality in general.
In metformin, Dr. Bilusic and colleagues saw a possible alternative to androgen deprivation therapy, also called chemical castration. While this common treatment can dramatically extend patients’ lives, the side effects are often brutal.
In the study, which followed 29 patients, the team gave patients metformin for eight weeks and then combined it with bicalutamide, an approved prostate cancer therapy, for an additional six months. While the study found no therapeutic advantages to adding bicalutamide, the reduced PSA numbers with metformin alone were intriguing.
“The PSA numbers were down in 40% of the cases,” said Dr. Bilusic. “Patients lost weight and they did not need castration during their time in the study, which is really important for their quality of life. We also saw beneficial effects for the immune system.”
The authors note that this early-stage study used a relatively low dose of metformin and the patient population all had body mass indexes above 25. Testing higher doses in different populations might produce better results.
These results show metformin may hold significant promise for patients, helping some avoid chemical castration. However, there are still many questions that need to be answered before the drug can be used to treat prostate cancer.
“These results show modest benefits, but we need to understand why,” said Dr. Bilusic. “There are four or five different mechanisms that could account for the lowering PSA numbers in these patients, and the next round of research will investigate that further. Nobody knows how this works, yet. However, we do know that some cancer patients taking metformin live longer, and that’s a great place to start.”
