A recent study found an inverse association between the joint use of metformin and testosterone replacement therapy (TTh) and incident hormone-associated cancers, such as prostate and colorectal cancers, among older White and Black men.
According to the study researchers, “it is plausible that metformin and TTh can work together as the prevalence of testosterone deficiency and diabetes has increased among older men, and subsequently their treatment with TTh and metformin. Previous studies have suggested a biological interaction between low levels of testosterone and type II diabetes, and subsequently between a Low T program and metformin.”
This study looked at 143,035 men aged 65 or older diagnosed with incident hormone-associated cancers from the SEER-Medicare 2007-2015 database. This included 110,430 White men, 13,520 Black men, and 19,085 of other race.
The researchers evaluated pre-diagnostic prescription of metformin and TTh using Medicare Part D National Drug Codes and Current Procedural Terminology codes. Results were published in Clinical Endocrinology.
There was an independent and joint association of metformin and TTh with incident prostate (odds ratio [OR]=0.44; 95% CI, 0.36-0.54) and colorectal cancer (OR=0.47; 95% CI, 0.34-0.64). No association was seen for male breast cancer, but the researchers acknowledged that it was a small sample size.
“In general, the combination of metformin use and TTh showed greater reduced effects of prostate and colorectal cancers and HRCs than the independent associations of metformin and TTh,” the researchers wrote.
Similar reduced associations were seen with White, Black and Other Race men.
According to the researchers, because the study used data from Medicare claims the results may not be generalizable to research cohorts using other types of insurance or no insurance at all.
“Future and larger studies need to confirm the independent inverse association of TTh and the joint inverse association of TTh plus metformin with these cancers in understudied populations,” the researchers concluded.