In my practice as a physician, I have had numerous patients who have declined starting on new diabetes medications due to articles in the news linking certain diabetes medication with cancer. Every drug (even aspirin) has a risk and a benefit and all people with diabetes should carefully weigh their options. However, the media can also be misleading when it comes to headlines, so it is also important to make an informed choice.
What do we know?
People with type 2 diabetes have an increased risk of certain cancers.
In the past 50 years, research has identified that there is an increase in certain cancers in people with diabetes (largely type 2), such as liver, pancreas, endometrial (lining of the uterus), colon, breast and bladder. Prostate cancer is less frequent in men with diabetes.
So, any study that just “observes” people with diabetes on new medication will see an increase in cancers compared to the general population, as the baseline rate of cancer is higher.
Which risk factors are common to both diabetes and cancer?
The development of cancer and diabetes may have some risk factors in common such as aging, obesity, lack of physical activity, poor diet, alcohol intake and smoking.
Which risk factors can people with diabetes do something about?
You can’t do much about your age, but other risk factors can be modified.
Obesity is a significant risk factor for especially breast and colorectal cancer, while a diet low in red and processed meats and high in fruits and vegetables is good for both cancer prevention and better diabetes management.
Minimal alcohol intake and not smoking lessens cancer risk and improves diabetes complication risks. Studies consistently show that higher levels of physical activity are associated with a lower risk of colon and postmenopausal breast and endometrial cancer. So, people with diabetes can lower their risk of cancer by looking at their lifestyle.
Moreover, like anyone else, people with diabetes should also undergo appropriate cancer screening for their risk factors and age.
Are there any diabetes medications that have been shown to cause cancer in humans?
To date there have been no randomized trials that have shown a strong link between a specific drug for treating diabetes and cancer.
Metformin: Currently, there have been no randomized trials that have shown a link between a specific drug for treating diabetes and cancer. The good news is that observational studies seem to link metformin with a lower incidence of cancer. A recent randomized trial looked at using metformin in patients with breast cancer. The survival overall was no better; however, a subgroup did benefit.
Recent studies testing metformin for cancer treatment haven’t been very positive. These trials were conducted quickly without carefully considering which patients might benefit most, how metformin works against cancer, or how best to combine it with other treatments. However, there is still hope. Research on using metformin in specific groups of patients, especially in combination with immunotherapy or as a preventive measure against cancer, needs to be conducted with better planning and design.
Insulins: Insulins are studied prior to release to be sure they do not promote abnormal growth of cells. Some observational (not randomized) trials have shown a link for people who have diabetes and are at higher risk for some cancers, may have a higher incidence of cancer, if on insulin. However, this may not be cause and effect from the insulin. There appears to be a link with those who have high insulin resistance having higher endogenous (produced in the body) levels of insulin and cancer, but there are no randomized studies that show a link between exogenous insulin (administered by injection) and cancer. There is a study in type 1 diabetes where higher doses of insulin were not linked to cancer.
DDP-4 Inhibitors: DDP-4 inhibitors, examples including sitagliptin (Januvia®), linagliptin (Trajenta®), saxagliptin (Onglyza®), have been shown to have a neutral effect on cancer risk, except for colorectal cancer, where the drug is associated with significantly reduced risk.
SGLT-2 Inhibitors: Although there were initial concerns about the risk of breast and bladder cancer with SGLT-2 inhibitors such as Jardiance®, recent evidence has shown no increased cancer risk among patients using this medication. Early studies have even shown an increased survival rate for patients with non-small cell lung cancer and pre-existing diabetes who take an SGLT-2 inhibitor, though these findings require further investigation.
GLP-1 Agonists: There has been some concern about the newer class of drugs called GLP-1 agonists and its potential link to pancreatitis, and with repeat pancreatitis, pancreatic cancer. The current research has shown that there was no elevated pancreatic, thyroid, and overall cancer risk in GLP-1 users.
So, the bottom line is that, at present, concern about cancer risk should not be a criteria for selecting treatment for type 2 diabetes.
