Lee Greer, a 54-year-old father of four and IT specialist in Houston, doggedly tried to make the best of his situation when he was diagnosed with Type 2 diabetes in 2010. He consulted with experts, changed his diet and got a trainer at the gym.

In 2012, with his diabetes under control, Greer got more unwelcome news. He learned he had stage III Hodgkin lymphoma, an immune system cancer, within a few days of his 53rd birthday.

First-line treatment for Hodgkin lymphoma typically includes combination chemotherapy, which can be hard for anyone to endure. “At the time, I didn’t know anything about chemo except that I didn’t want anything to do with it,” he recalls.

For people who have diabetes, like Greer, cancer treatment can be a tricky balancing act of managing the diabetes while treating the cancer. Both diseases affect the body’s metabolism, which is how cells turn food into fuel. And they affect many of the same biological processes. That means diabetes medications can alter or even enhance the effectiveness of cancer treatment. Meanwhile, cancer treatments can exacerbate the blood sugar problems that characterize diabetes.

The diabetes-cancer link is becoming a growing public health concern. In one small study, published in 2002 in the Journal of Surgical Research, between 8 and 18 percent of cancer patients had diabetes at the time of diagnosis.

The Link

Epidemiological studies show a solid link between diabetes and cancer. A person with Type 2 diabetes faces at least twice the risk for being diagnosed with liver, pancreatic or endometrial cancer as people without Type 2 diabetes, according to an extensive analysis of existing studies published in 2009 in Endocrine-Related Cancer. For colorectal, breast, kidney and bladder cancers, as well as some lymphomas, the risk increases between 20 and 50 percent compared with people without Type 2 diabetes. Epidemiological studies also show that people with diabetes face a higher risk of death from cancer than people without diabetes.

The diseases share a host of risk factors, including being overweight or obese, having low levels of physical activity, and smoking tobacco. Scientists also suspect there is a biological connection between cancer and diabetes, although the specific mechanisms are unclear. (See A Dangerous Duo.) But it is becoming more important for doctors and researchers to figure out the connection: As many as one in nine people age 20 or older in the U.S., or up to 24 million people, have been diagnosed with Type 2 diabetes, which accounts for between 90 and 95 percent of adult diabetes cases. Experts estimate that millions more have the disease but have not been diagnosed, and the number of people diagnosed has risen every year.

For those who find themselves in the stressful situation of having these two serious diseases at once, getting a firm grip on managing their diabetes while being treated for cancer is critical, says Sonali Thosani, a clinical endocrinologist who specializes in treating cancer patients with diabetes at the University of Texas M. D. Anderson Cancer Center in Houston. With proper glucose monitoring, attention to diet and exercise, and expert advice, patients can improve the likelihood of maintaining quality of life during and after cancer treatment.

A Dangerous Duo

Having diabetes and cancer increases mortality risk.

For more than 50 years, researchers have observed that cancer and diabetes not only go hand in hand, but that having diabetes increases a person’s risk for dying from cancer. Recent studies have begun to quantify that connection, but so far they haven’t mapped out exactly why there is a relationship.

The latest results from the Cancer Prevention Study II (CPS II), a 26-year mortality study that enrolled more than a million adults in the U.S., show a significant association between diabetes and cancer mortality for many kinds of cancer.

Reporting the latest CPS II findings in Diabetes Care in 2012, researchers suggest that the increase in mortality may be influenced by overlapping biological mechanisms of the two diseases that combine to cause greater harm. It’s also possible that people with both diseases may not seek or receive adequate health care compared with the greater population.

“The studies are interesting and compelling, but they don’t necessarily get to the root of the cause-and-effect relationship of the conditions,” says biomolecular engineer Jamey Young, who studies the molecular connections between the two diseases at the Vanderbilt University School of Engineering in Nashville, Tenn.

In some ways, he says, the diseases are mirror images of each other. Cancer cells begin as healthy cells that proliferate out of control, and rapid growth requires glucose as fuel. To get the glucose they need, cancer cells corrupt the proteins that normally control the influx of glucose into the cell.

Diabetes involves some of the same cellular mechanisms, “but in the opposite direction,” Young notes. The body’s tissues don’t take up as much glucose as they should. “Cancer cells take up glucose faster than a normal cell would, but in diabetes they don’t take up glucose as fast as they should.”

That connection may help explain why metformin, the safe and inexpensive drug widely used to treat diabetes, has been connected with reduced risk for some types of cancer in people with diabetes, says Young.

However, “the jury’s still out” on why it is beneficial with respect to cancer, he says. Once researchers figure out how metformin works against cancer, they can identify patients most likely to reap some anti-cancer benefit.

Get Good Information

After Greer was diagnosed with cancer, he read everything he could find—a typical reaction for a newly diagnosed patient. But not everything online can be trusted, which means that left on their own, patients may get misinformation about their disease.

“It’s kind of a tightrope,” Greer says, “because you don’t want to go into treatment completely ignorant.”

Thosani, who treated Greer, recommends that patients check with an experienced endocrinologist for the latest, most accurate information about how cancer treatment can influence diabetes care. “There’s a lot of information for the general public that is hard to interpret and filter,” she says.

To learn more about diabetes, Thosani advises her patients to stick with trusted sources. The website of the American Diabetes Association has reliable information, as well as diet tips and meal plans, she says. In addition, many hospitals offer weekly community classes where patients can get tips and recommendations from diabetes educators.

Measure More

Tracking patterns and fluctuations in glucose levels is one way patients can actively participate in their own care, says Janice Baker, a nutritionist and registered dietitian at Baker Nutrition in San Diego who works with diabetes and cancer patients. Glucose is a naturally occurring sugar that provides fuel to cells, which use the hormone insulin to retrieve glucose from blood. In Type 2 diabetes, the body becomes insulin-resistant or doesn’t produce enough insulin, meaning glucose accumulates in the blood. About 25 percent of people with diabetes are treated directly with insulin, but most take an oral medication to keep levels of blood glucose, sometimes called blood sugar, under control.

“Patients will come to us and ask, ‘Why is it important to monitor my sugars when I have cancer?’ ” Thosani says. The reasons are straightforward. Chemotherapy is often given with heavy doses of steroids to lessen nausea, but steroids can cause a person’s blood sugar to spike. Radiation, too, can boost glucose levels. People with diabetes may need additional insulin injections during treatment—Greer did—and nondiabetic patients may develop “secondary diabetes,” where glucose levels rise during individual cancer treatments.

In addition, high glucose levels can thwart cancer treatment. High sugars increase a person’s likelihood of getting an infection after surgery, Thosani says, and surgery may be delayed if those levels are too high. Clinical trials often require patients to have normal glucose readings if an experimental treatment is known to cause hyperglycemia, or elevated blood sugar levels.

Greer was already monitoring his glucose and following a diet and exercise regimen for his diabetes when he was diagnosed with Hodgkin lymphoma. But the cancer diagnosis meant even more frequent monitoring. His first cancer treatment, in fall 2012, was a chemotherapy combination called ABVD (Adriamycin [doxorubicin], bleomycin, vinblastine, dacarbazine), and doctors or nurses checked his blood sugar levels before those treatments. Initial scans, taken three months into treatment, looked promising. His cancer was not gone, but it was reduced drastically.

After his second follow-up CT scan showed that he’d had a resurgence of his cancer in January 2013, Greer received a chemotherapy combination called ICE (ifosfamide, carboplatin, etoposide) followed by a stem cell transplant. During this procedure, which is standard treatment for Hodgkin lymphoma patients with recurrent disease, a patient receives an infusion of stem cells—the ones that produce blood cells—to replace those killed during intense chemotherapy.

Reducing Cancer Risk for People With Diabetes

Cancer screening in those with diabetes.

If you have Type 2 diabetes, you are at higher risk of being diagnosed with liver, pancreatic, endometrial, colorectal, breast, kidney or bladder cancers, as well as some lymphomas, than someone without Type 2 diabetes. That’s not necessarily because diabetes causes cancer; the diseases have similar diet and lifestyle risk factors, which include smoking, lack of exercise and poor diet.

“When I see people individually and they’re newly diagnosed with diabetes, I tell them to focus on the ABCs,” says Janice Baker, a registered dietitian and nutritionist in San Diego who treats patients with diabetes and cancer. A stands for the A1C test, a blood test that shows a person’s glucose levels over the past three months. B stands for blood pressure, and C stands for cholesterol.

The best way to maintain normal levels of the ABCs, she says, is to eat right and exercise. “If you get better control of glucose and weight, your cancer risk will go down.”

In recent years, researchers have begun to suggest cancer screening for some people with diabetes. In particular, elderly people newly diagnosed with Type 2 diabetes who have lost weight and have no family history of diabetes may be at higher risk for pancreatic cancer, which is most often diagnosed at an advanced stage. No screening tests exist for pancreatic cancer, and available blood tests only detect disease at a late stage.

Sonali Thosani, a clinical endocrinologist at M. D. Anderson Cancer Center in Houston who specializes in treating patients with cancer and diabetes, says there is little evidence for a general rule “that anyone diagnosed with diabetes should get screened for cancer.” However, for people at higher risk who have symptoms that raise a doctor’s level of concern, “I think cancer screening is a good thought, and it could help,” she adds.

Make a Plan

During treatment, food can become a tremendous source of stress, Baker notes. Cancer treatment can change a person’s sense of taste, decrease appetite and cause nausea, all of which can make it difficult to get through a meal. But having a diet plan in hand and a registered dietitian who can give advice may help.

“I recommend people try to work out a nutrition plan to try to maintain their strength, health and weight after treatment,” Baker advises. “The earlier the better.”

Thosani says she gives her patients straightforward information about lifestyle choices and health maintenance. “We talk about exercise. Studies have shown that exercise benefits patients with cancer in many ways,” she says. “A large part of our patient population is obese, and studies show obesity is associated with insulin resistance. So we talk about weight loss and make a plan that’s tailored to the patient.”

Greer says that when he was first diagnosed with diabetes, his primary care doctor didn’t tell him exercise could help bring down blood sugar levels. But over time, he saw how diet and fitness could improve his life. Because he was having trouble breathing, he resolved to go back to the gym and exercise as much as possible after he finished cancer treatment. It wasn’t easy.

“My trainer had me do lunges, but after five steps I needed five minutes to recover,” he says. “The next week, I did it again.” And the lunges came easier, week by week.

Greer says his experience—he has had no evidence of cancer since May 2013—has given him a new perspective on the uniqueness of two diseases that nonetheless share a deep biological link.

For diabetes patients faced with a cancer diagnosis, he says, it’s important to remember that a person’s cancer treatment may need to be changed to keep blood sugars in check—and diabetes medications can be adjusted to anticipate and react to blood sugar changes resulting from cancer treatment.

“There’s no one-size-fits-all treatment for everyone,” Greer says. “What happened to someone else doesn’t always apply” to newly diagnosed patients. “Every person should get treatment that’s individualized.” 

Stephen Ornes is a contributing writer and a reporter-researcher for Cancer Today. He lives in Nashville, Tenn.