April 13, 2016

More studies are finding a higher rate of certain cancers, such as breast, colon and liver, among people with diabetes. Some of the research focuses on the drugs used to treat diabetes, since they regulate insulin and growth factors that are also involved in tumor growth.

In an animal study published in Science Translational Medicine, researchers report that antioxidants in some diabetes drugs may be responsible for spreading tumors.

The study was conducted in mice, but it points to a possible mechanism to explain why cancer rates are higher among certain people with diabetes. Antioxidants are typically recommended to prevent cancer, since they fight the free radicals that can trigger tumor growth. But in this case, say the study authors, the protection from further oxidative stress—which is what antioxidants do—may actually insulate cancer cells, making it easier for them to spread to other parts of the body.

Hongting Zheng, from Xinqiau Hospital and the Third Military Medical University, says that the drugs, belonging to the dipeptidyl peptidase-4 (DPP-4) inhibitor class—there is a list of FDA approved DPP-4 inhibitors here—did not increase the formation of new cancers, but did promote the spread of existing colon and liver tumors in the mice studied.

Zheng said in email to TIME that the effect may also be more pronounced among certain people with genetic predisposition to the effects of oxidation. All the more reason that “understanding the effects of antidiabetic agents on tumor biology is indispensable for the development of specialized drug therapy that is safe for treating diabetic patients with cancer.”

For now, he says, these drugs that contain antioxidant properties “may need to be administered with caution in diabetic patients with existing cancer.”

More research will be needed to determine which people should or shouldn’t be taking these medications.

Contact us at editors@time.com.

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