WHI Informs on Links Between Diabetes, Metformin, and Cancer

Medscape
 
A new analysis from the Women's Health Initiative (WHI) shows that, compared with women without diabetes, adult postmenopausal women with type 2 diabetes are at a significant 13% increased risk of invasive cancer and have a 46% higher risk for cancer death.
The latest WHI data, reported in the April 15 issue of the International Journal of Cancer, also suggest that long-term metformin therapy — the first go-to medicine for type 2 diabetes — may be linked with a reduced risk of cancer mortality.....

But Does Metformin Really Reduce Cancer Deaths?
 
Dr Fonseca explained to Medscape Medical News that it is difficult, in the WHI, to determine whether metformin may reduce the risk of cancer mortality in a realistic sense.
He feels that the message this kind of study sends is that other drugs used to treat diabetes are "bad," which is not true.
"Metformin is standard therapy and is typically used in relatively healthy individuals, while other medications are used in patients with progressive diabetes; in short, in sicker patients," he noted.
Dr Horton agreed. "Indeed, metformin is contraindicated in patients with significantly impaired kidney function," he said.
Sicker patients have additional comorbidities that may well contribute to the risk of cancer and cancer mortality, Dr Fonseca pointed out.
"Randomized studies have not shown that other drugs used to treat diabetes are associated with a higher risk for cancer mortality," he added......

And another endocrinologist warns about interpretation of this type of work. "Such studies [as the WHI] need to be viewed with caution," Vivian A Fonseca, MD, Tullis–Tulane Alumni Chair in Diabetes and chief of the section of endocrinology at Tulane University, New Orleans, told Medscape Medical News .

Dr Fonseca explained that studies linking diabetes and cancer and metformin use with decreased cancer mortality are confounded by selection bias and lack of randomization.