Diabetes and cancer: what’s the real connection?

If you’re living with diabetes, you might know all about the intriguing and intricate relationship between diabetes and certain types of cancer. And it’s not a one-way street — the connection goes both ways.

So, what does current research say about this bidirectional relationship? Why are some cancer survivors more likely to develop diabetes? And why is understanding the difference between new-onset and long-standing diabetes critical in cancer detection and care?

Which cancers are linked to diabetes?

It’s been known for some time that diabetes, especially type 2 diabetes, can increase the risk of several types of cancer. But which cancers specifically?

According to a growing body of evidence, people with diabetes are more likely to develop pancreatic, liver, colorectal, breast and endometrial cancers. Why these cancers in particular? Different factors may be at play:

• People with type 2 diabetes often have higher circulating insulin levels, which may promote the growth of cancer cells.
• Long-term low-grade inflammation, common in diabetes, can create an environment in the body that’s more vulnerable to cancer development.
• Persistently high glucose levels may not only damage blood vessels and organs but also contribute to tumour growth.

A 2025 review in Seminars in Oncology outlines these mechanisms in detail, underscoring that this isn’t just correlation, but that there’s a plausible biological basis linking diabetes to cancer risk.

The gender gap in diabetes-related cancer risk

Diabetes doesn’t affect everyone’s cancer risk in the same way. In fact, research shows that women with diabetes tend to have a higher overall risk of developing cancer than men with diabetes. Across many different cancer types, the relative increase in cancer risk associated with diabetes was greater in women. Importantly, this wasn’t limited to a single cancer. Instead, diabetes appeared to place a broader cancer burden on women overall.

So why might this difference exist? The answer is likely complex and involves a mix of biological and lifestyle factors. Many of the risk factors shared by diabetes and cancer, such as excess body weight, physical inactivity and smoking, can worsen insulin resistance and promote long-term inflammation in the body.

These changes can also disrupt hormone regulation, all of which are processes linked to cancer development. Some evidence suggests that these metabolic and lifestyle effects may be more pronounced, or persist for longer, in women with diabetes. Over time, this may help explain why women experience a greater relative increase in cancer risk compared with men, even when both are living with the same condition.

Can cancer treatments cause diabetes?

Interestingly, the relationship works the other way, too. People who have survived cancer, particularly those treated with certain therapies, are at greater risk of developing new-onset diabetes after cancer.

A recent article published in Annals of Medicine and Surgery (2024) explored how cancer treatments, while life-saving, can disrupt glucose metabolism in various ways. Here are a few examples:

• Chemotherapy and corticosteroids, often used to manage cancer or treatment side effects, can cause spikes in blood sugar.
• Androgen deprivation therapy (used in prostate cancer) has been associated with insulin resistance.
• Abdominal radiation, particularly in children and young adults, can damage the pancreas, impairing insulin production.

This risk is beyond a simple short-term issue during treatment. For many survivors, diabetes may not appear until months or even years later. And because cancer follow-up typically focuses on recurrence and surveillance imaging, blood glucose levels might not be closely monitored unless there’s a specific concern.

It’s not just a case of better detection

You might ask whether there is simply an increase in diabetes and cancer diagnoses because we’re looking more closely. After all, both conditions are common, and frequent medical visits often lead to more testing. But experts now agree this is more than just detection bias. A growing number of studies demonstrate a biologically plausible connection between the two conditions.

For instance, shared risk factors, such as obesity, sedentary lifestyle, poor diet, and inflammation, as well as treatment-related effects that support this real, bidirectional link. Although these shared risk factors present a more complex picture, the association between diabetes and certain cancers remains.

That means clinicians are not just diagnosing more people by chance. There is a real link that has clinical implications for diabetes management and cancer care.

New-onset vs long-standing diabetes: a new focus in research

Here’s where it gets even more interesting. Researchers are now focused on distinguishing new-onset diabetes, especially in older adults, as a potential early marker of underlying cancer, particularly pancreatic cancer.

Why pancreatic cancer? Because in many cases, new-onset diabetes can precede the cancer diagnosis. The pancreas is central to both insulin production and tumour development, and a pancreatic tumour can impair insulin secretion, sometimes months before the cancer is detected.

So, while long-standing diabetes may increase the risk of developing certain cancers over time, sudden-onset diabetes, especially in someone with no history of obesity or insulin resistance, could be a red flag. This is especially important because pancreatic cancer often presents late and has poor survival outcomes. Early detection can make a big difference.

In fact, healthcare systems are exploring screening programmes that use new-onset diabetes in people over 50 as a trigger to investigate for pancreatic cancer. It’s a promising area of research that could lead to earlier diagnoses and better outcomes.

What does this mean for people living with diabetes or cancer?

Understanding this bidirectional relationship matters for individuals and healthcare providers.

• If you have diabetes: Regular cancer screenings, especially for colorectal, breast, and liver cancers, may be more relevant than ever. Maintaining good glycaemic control, staying active and managing weight could help reduce your risk.
• If you’re a cancer survivor: Keep an eye on your blood glucose levels, even years after treatment. If you were exposed to chemotherapy, steroids, radiation, or hormone therapy, you may have a higher chance of developing diabetes, and early diagnosis is key.
• If you’re newly diagnosed with diabetes in your 50s or older: Talk to your GP about whether further investigation might be needed, particularly if you don’t fit the type 2 diabetes profile. It might be nothing, but it’s worth checking.

What’s next in research?

The complex interaction between diabetes and cancer is now one of the most dynamic areas of medical research. With a better understanding, there’s hope that:

• Cancer therapies are refined to reduce metabolic side effects.
• New-onset diabetes can serve as a valuable biomarker for early cancer detection.
• Strategies are developed to prevent diabetes in cancer survivors through tailored screening and lifestyle support.

It’s a reminder that in medicine, everything is connected, and sometimes the clues to one condition or disease lie in the symptoms or progression of another.

Should people with diabetes be alarmed?

Living with diabetes doesn’t mean you’re destined to develop cancer, and not all cancer survivors will go on to develop diabetes. But recognising the links between these conditions can empower you to take preventive action, ask informed questions, and work with your healthcare team for more personalised care.

After all, the more we understand how diseases interact, the better we can treat and prevent them.