Research links the two diseases, a double whammy that raises even more health risks, but survivors can manage the chronic condition.
Caren DeSantis wasn’t surprised when tests showed that she had dangerously high blood sugar levels. “I had added 30 pounds onto my petite frame in less than six months, and I knew the extra weight wasn’t good for me,” says the Fort Worth, Texas, resident. DeSantis has always struggled with her weight, but the pounds really added up in October 2013.
That’s when DeSantis, then age 48, began taking steroids to keep nausea at bay while undergoing chemotherapy to treat stage 3c endometrial cancer. “It seemed crazy that I was getting bigger while feeling sick and having little appetite, yet I seemed to gain weight overnight,” she says. “And I was too wiped out from the cancer treatments to even think about exercising.”
As soon as DeSantis completed her treatments — surgery, six rounds of chemotherapy and 33 targeted radiation treatments to her pelvic region — she turned her focus to improving her overall health. She fixed nutritious meals and was constantly on the move, chasing after her active toddler daughter. She also started volunteering at Cancer Hope Network, a national nonprofit organization that pairs support volunteers with other people affected by cancer. Slowly, the blood sugar numbers crept down, but in 2015 the cancer came back, this time in the para-aortic lymph nodes near her left kidney. “After (I underwent) more radiation treatments, my blood sugar was off the charts no matter what I did,” says DeSantis, who received a type 2 diabetes diagnosis. “That diagnosis wasn’t as devastating as cancer, but managing another chronic illness is definitely a challenge.”
THE CANCER-DIABETES CONNECTION
Up to 18% of people with cancer also have diabetes, a double whammy that makes a person even more susceptible to heart disease, stroke, kidney problems, nerve damage and neuropathy, or numbness or tingling in the hands or feet. The most common form of diabetes, type 2, makes the body resistant to insulin, a pancreatic hormone that helps blood sugar, or glucose, enter cells so the body can use it for energy. When cells resist insulin, glucose stays in the blood, building to unhealthy levels that can damage blood vessels and nerves.
An online search for diabetes risk factors will turn up a list of contributors such as excess weight, sedentary lifestyle, family history and age — people over 45 are more likely to have the disease. But one risk factor is seldom mentioned: cancer.
Study findings suggest that the incidence of diabetes is six times greater among people with cancer compared with those who don’t have cancer. Results of a 2018 JAMA Oncology study showed that cancer survivors are more likely to develop diabetes within two years of completing cancer treatments, although the risk remains elevated throughout a survivor’s lifetime. Perhaps unsurprisingly, people with cancer of the pancreas, the organ that makes insulin, are five times more likely to develop type 2 diabetes than people with similar risk factors and no history of cancer.
Diabetes odds nearly double for people with kidney or liver cancer. Still, experts caution that diabetes isn’t necessarily triggered by a certain type of cancer. Instead, it’s more likely that certain cancer treatments are responsible for raising blood sugar levels. The longer those levels stay elevated, the greater the chances of diabetes. Unfortunately, many cancer-fighting treatments are linked to diabetes. “Steroids mitigate nausea and other chemotherapy side effects and are a huge help in getting a patient through potentially lifesaving treatments,” says Dr. Azeez Farooki, an endocrinologist at Memorial Sloan Kettering Cancer Center in New York City.
“The downside is that people who take steroids often gain weight that can be hard to lose. Steroids also raise blood sugar, although this effect is usually temporary and goes away when steroid use stops.” Radiation treatments, whether whole-body therapy to treat blood cancers or targeted to the abdominopelvic region where the pancreas is located, may also destroy insulin-producing cells, he says.
There is also a correlation between diabetes and immunotherapies, such as those commonly used to treat kidney, lung and blood cancers. “Research suggests that approximately one out of 110 people who take immune checkpoint inhibitors (anti-PD-1 or anti-PD-L1) develops sudden and often severe onset of diabetes, requiring insulin treatments,” says Dr. Victor Lavis, a professor in the department of endocrine neoplasia and hormonal disorders at The University of Texas MD Anderson Cancer Center in Houston. Experts think the treatment triggers an attack not just on cancer cells but also on critical insulin-producing beta cells found in the pancreas.
Low estrogen levels may explain why women who are postmenopausal or in medically induced menopause because of certain treatments for breast or gynecologic cancers are more prone to diabetes. In one study out of the Women’s College Hospital in Toronto, nearly 10% of post- menopausal breast cancer survivors developed diabetes within six years of finishing cancer treatments.
Age may also play a role. The Centers for Disease Control and Prevention (CDC) estimates that more than a quarter of people 65 and older have diabetes. “As individuals get older, their risk for developing diabetes goes up regardless of whether they’ve had cancer,” says Denise Soltow Hershey, a family nurse practitioner and associate professor at the Michigan State University College of Nursing. Hershey, who also holds a Doctor of Philosophy in nursing, conducts research on diabetes and cancer.
Finally, the stress from managing a chronic disease like cancer, combined with angst-inducing situations like hospitalization, surgery, infection and fear of the unknown, can flood the body with cortisol. This steroid hormone causes stored energy to be released and converted into glucose that is released into the bloodstream.
PREVENTING DIABETES AFTER CANCER
Although these links are cause for concern, cancer does not always lead to diabetes.
“Regardless of cancer history, anyone can lower the risk of diabetes by being active, eating a healthy diet that is high in fiber and low in fat, and maintaining a healthy weight,” Hershey says. Because obesity raises the risk of diabetes and cancer recurrence, a healthy weight is key to staving off both diseases.
This doesn’t call for extreme measures: Dropping just 5% to 7% of excess weight and fitting in 150 minutes of physical activity every week can cut diabetes risk by nearly 58%, and that number jumps to 71% for people over 60, according to CDC research.
If a person’s blood sugar was elevated during cancer treatments, Farooki recommends blood sugar tests every six months for the first year after completing therapy. The American Diabetes Association recommends annual screenings for individuals at high risk of diabetes, or every three years for those at average risk. “There is a definite need for more aggressive diabetes screenings and disease prevention strategies for cancer survivors,” Farooki says.
The CDC estimates that more than one in three Americans have prediabetes, meaning their blood sugar levels push perilously close to a type 2 diagnosis. But 80% of people with prediabetes are unaware that they have the condition, so they miss out on opportunities to make proactive lifestyle changes that could halt disease progression.
There are several ways to screen for diabetes. The fasting plasma glucose test assesses blood sugar levels after the patient has gone without food and drink (excluding water) for at least eight hours. Results between 100 and 125 milligrams per deciliter indicate prediabetes.
A healthy number is anything below 99, whereas anything above 126 is considered diabetes.
Another blood test, hemoglobin A1c, provides an average of a person’s blood sugar levels over a period of two to three months. An A1c reading of 6.5% or higher indicates diabetes. A healthy level is less than 5.7%. The test is more convenient because it doesn’t involve fasting. However, preliminary findings from a study conducted at City of Hope’s Diabetes & Metabolism Research Institute in Duarte, California, suggest that the A1c test misses up to 73% of diabetes diagnoses compared with the oral glucose test.
In addition to getting routine blood tests, it’s important to be on the lookout for signs of diabetes: frequent urination, especially at night; increased thirst; unexplained weight loss; and blurred vision. “Many people with cancer experience ongoing symptoms of fatigue and neuropathy,” Hershey says.
“While these problems may be related to cancer treatments, they should not be dismissed, because they may also indicate diabetes.” It’s important to call a doctor if a person notices any warning signs of diabetes, including worsening problems like fatigue and neuropathy.
LIVING WITH DIABETES
Diabetes contributes strongly to cardiovascular disease, the second leading cause of death for people with cancer — and probably the leading cause for people who have survived cancer for 10 years or more, so it’s vital to keep blood sugar levels in check. Elevated glucose levels can damage blood vessels, making people with diabetes twice as likely to experience heart disease or stroke. In addition, cancer survivors who have diabetes and don’t control their blood sugar report a lower quality of life in part because symptoms like pain and fatigue tend to be more severe. Poor blood sugar control also raises the risk of cancer recurrence, especially among breast cancer survivors.
Endocrinologists typically turn to metformin, a prescription oral medication, as the first line of treatment. “We treat diabetes the same regardless of whether you’ve had cancer or are currently going through cancer treatments,” Farooki says. “The goal is to bring blood glucose levels as close to normal as possible through healthy lifestyle changes and medications, if needed.”
Renita Michael takes Janumet, a combination of metformin and Januvia (sitagliptin), to manage diabetes that occurred after she had surgery and isotopic radiation therapy for stage 3 thyroid cancer in 2006. Michael, a resident of Hillsborough, New Jersey, was 36 at the time. “I was already seeing an endocrinologist for thyroid problems, so the diabetes was quickly detected,” she says.
Even with medication, Michael’s blood sugar remains high. It doesn’t help that she’s now recovering from lumpectomies performed in 2017 and 2019 after the cancer spread to her breasts. “I try to watch what I eat, and I get blood tests every three months to help my doctor deter- mine the best treatment,” she says.
Eventually, Michael may need to do daily finger sticks to check her blood sugar and administer insulin injections. Although the idea of managing another lifelong illness is unsettling, Michael is grateful that diabetes is treatable. “My family has a history of heart disease,” she says. “I’m focused on doing what I can to protect my health and heart.”