Diabetes as a side effect of cancer treatment: 8 things to know

Diabetes affects roughly 10% of people in the United States. Another 1 in 3 has pre-diabetes, or elevated blood sugar levels that don’t quite reach the threshold for diabetes.

Often, diabetes develops on its own. But sometimes it can stem from an underlying cancer — or even be a side effect of the therapies used to treat it. When diabetes is caused by something else, it’s known as secondary diabetes.

We checked in with diabetes specialist Sonali Thosani, M.D., to learn about this potential side effect of cancer treatment, and what — if anything — can be done to reverse it.

How common is it for cancer patients to develop secondary diabetes as a result of their treatment or its side effects?

That’s hard to say, for a few reasons. The first is that a lot of patients come to MD Anderson with undiagnosed diabetes. That means they already have it, but they don’t know it yet, because in some cases they haven’t been to see a doctor in years.

Another reason is that not every patient gets their blood sugar levels checked right away. Sometimes, the first evaluation of that happens before they go into surgery, or after they’ve already started cancer treatment.

Many of our patients are also receiving steroids to improve their ability to tolerate chemotherapy, and high blood sugar is a known side effect of steroids. So, it’s challenging sometimes to distinguish between the patients who already had diabetes before they came to MD Anderson and the ones who developed it after they arrived.

That being said, about 23% of our hospitalized patients at MD Anderson have an established diabetes diagnosis, whether it’s Type 1, Type 2 or secondary.

What’s the difference between Type 1 and Type 2 diabetes?

Type 1 diabetes is when a person’s immune system makes antibodies against the pancreas. This damages the organ and keeps it from working properly. Type 1 diabetes usually shows up in young teens, but it can also happen in adults in their 50s and 60s. These patients require insulin long-term, as well as other lifestyle changes, such as carbohydrate counting, frequent finger sticks, and diet adjustments to prevent ketoacidosis, a life-threatening condition where blood sugar levels rise extremely high.

Type 2 diabetes is much more common and can be diagnosed at any age. It’s usually associated with obesity and/or insulin-resistance, and can be managed with a combination of diet, exercise and medication. Most patients with Type 2 diabetes will start out on an oral medication, but require insulin within 15 to 20 years of their diagnosis. There’s also a strong genetic component to Type 2 diabetes, so it often occurs in people whose parents or siblings have diabetes.

What’s the most common cause of secondary diabetes?

A number of things can cause secondary diabetes in cancer patients, including steroids, the surgical removal of part of the pancreas, and certain chemotherapy drugs and targeted therapy treatments. It can also be caused by diet, stress, inflammation or even uncontrolled pain.

Immune checkpoint inhibitors can also have a rare and irreversible side effect known as checkpoint inhibitor diabetes. While it’s not very common, we have seen cases of it here at MD Anderson. And it’s similar to Type 1 diabetes, but often unrecognized until a patient has life-threatening ketoacidosis.

That’s why getting care at a comprehensive cancer center like MD Anderson is so important: it equips you with a team of experts who can better detect rare complications like these in a timely manner.

How often is secondary diabetes permanent?

It’s not really that straightforward. If your blood sugar is only high because of steroids, it may return to normal once you stop taking that medication. Similarly, if it’s due to a neuroendocrine tumor, it may drop back down once the tumor is removed.

Most patients are going to recover from secondary diabetes, provided they didn’t have underlying diabetes to begin with. But if you have underlying diabetes or pre-diabetes, these things could absolutely stress your system to the point that it might never get back to normal.

And if all or part of your pancreas is removed, you’re always going to have some type of issue with glucose management, since you don’t have the complete organ needed to make insulin.

Can anything else be done to reverse secondary diabetes?

When secondary diabetes is caused by external factors, it often resolves once those factors are removed. In patients with underlying Type 2 diabetes, changes in diet, intentional weight loss and exercise can also help with improving glucose control.

But with permanent changes related to surgery, there may be no reversal of this condition.

Why is it important to control diabetes during cancer treatment?

For one thing, high blood sugar can cause dehydration. That, in turn, may increase the side effects patients experience from cancer treatment. High blood sugar can also prompt doctors to postpone surgeries, due to the greater risk of infection and delayed wound healing. And overall, patients with normal blood sugar just do much better in terms of outcomes and chances of recurrence, compared to those with high blood sugar levels.

Cancer patients with low blood sugar levels also are at greater risk of complications. Many cancer patients face challenges around maintaining their weight, due to appetite changes and nausea, so we see a lot of malnutrition. And if someone’s blood sugar drops really low, they could have a seizure or pass out and fall. If they also happen to be taking a blood thinner, they could bleed to death before anyone finds them.

So it’s really important to make sure your diabetes is managed during cancer treatment — and to go to a comprehensive cancer center like MD Anderson. Having this kind of multidisciplinary, patient-centered care really allows for better communication between the different specialists caring for you. We’re not just treating your cancer, but also any underlying conditions. And we’re taking into account how those might be affected by your cancer treatments.

How does MD Anderson manage cancer patients’ diabetes treatment?

We use the latest technology to help our patients manage their diabetes during cancer treatment. Continuous glucose monitors provide painless monitoring for many patients, especially those with chemotherapy-induced neuropathy, which can make finger sticks even more painful. We also use insulin pumps in patients who need multiple insulin shots a day.

But there’s no one-size-fits-all when it comes to glucose management in a cancer patient. So, we tailor each patient’s diabetes treatment.

Patients on clinical trials, for instance, might need their glucose levels to stay below a certain level in order to continue participating. Others might need their levels optimized so that they’ll have a lower risk of infection and heal more quickly after surgery. And for patients who have a poor prognosis, we might aim to provide them with comfort, rather than focusing on strict glucose control, to prevent the unpleasant symptoms of high or low blood sugar.

What’s the most important thing you want people to know about secondary diabetes?

It’s easy to feel overwhelmed when you’re facing two different diagnoses. But diabetes gives you an opportunity to take control in a way that cancer doesn’t. So, don’t lose hope.

Diet and lifestyle choices can often help you manage diabetes as you undergo cancer treatment, and these changes may also help you feel better. So, getting diabetes under control during cancer treatment is important – and possible.

Request an appointment at MD Anderson online or by calling 1-877-632-6789.