Cancer, diabetes and diabetes treatments……is there a link?

In the past year or so, 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, endometrium (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.

What risk factors are common to both diabetes and cancer?

The development of cancer and diabetes have some risk factors in common such as aging, obesity, lack of physical activity, poor diet, alcohol intake and smoking.

What 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 bowel 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.

Moderation in alcohol intake and not smoking lessens risk of cancer and also 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 link between a specific drug for treating diabetes and cancer. The good news is that observational studies seem to link metformin with lower incidence of cancer and at present metfomin is being studied to see if it improves survival in woman with breast cancer treated with chemotherapy.

Insulins are studied prior to release to be sure they do not promote abnormal growth of cells. A recent 5-year study called ORIGIN looked at Lantus insulin and cancer and no association was seen, although this particular study was really to look at heart disease and Lantus.  

There has been some concern about the new class of drugs called ‘incretins’. One type, GLP-1 agonist ( e.g. Victoza) was linked to thyroid nodules in rodents but this doesn’t appear to be a problem in humans. If a person has a personal or family history of a rare type of thyroid cancer (C- cell) they should not take this type medication. The other incretin agents (DPP-4 such as Januvia, Onglyza or Tradjenta) have been in the news about whether there is a relationship to pancreatitis and, with repeat pancreatitis, cancer risk. All the data was reviewed in June this year at the NCI (National Cancer Institute) sponsored symposium on incretins and pancreatitis and cancer, and there is not sufficient data to propose a link.

So, the bottom line is that, at present, concern about cancer risk should not be a criteria for selecting treatment for type 2 diabetes.