Nine years ago, Brenda Gray, a former schoolteacher in North Carolina, discovered she had Type 2 diabetes.
Since then, she has learned to manage the disease, diligently taking her medicine and keeping tabs on her blood sugar. But in September, she was told she had skin cancer, and her diabetes spun out of control.
Ms. Gray started an aggressive course of treatment that included radiation therapy. But the treatments weakened her and destroyed her appetite. Unable to eat, she developed dangerously low blood-sugar levels, and about two months ago, Ms. Gray’s daughter had to rush her to a hospital.
“She found me in bed shaking and sweating,” said Ms. Gray, who is 62 and lives in Durham. “When I got to the hospital, they couldn’t understand how I was still standing.”
Cancer and diabetes are two of the leading killers in America. Each can be a devastating diagnosis in its own right, but researchers are finding that the two often occur together. By some estimates, as many as one in five cancer patients also has diabetes.
In a recent joint report, the American Cancer Society and the American Diabetes Association noted that people with Type 2 diabetes have an increased risk of developing cancers of the liver, pancreas, colon and bladder. Researchers with the National Cancer Institute released a similar report last year, which found greater rates of cancer among diabetics, as well as an elevated risk of dying from cancer.
Experts say it is clear from accumulating clinical data that the two share some biological links. The problem results from simple demographics as well: with the rapid rise in Type 2 diabetes and a growing population of cancer survivors, the two diseases are coinciding more frequently in older patients.
“We are going to see a lot greater numbers of people with both diseases,” said Edward Giovannucci, a professor of nutrition and epidemiology at the Harvard School of Public Health and an author of the joint report. “By some estimates, the link between diabetes and cancer may quantitatively become even more important than the link between smoking and cancer.”
Already, oncologists say, it is not uncommon to encounter patients struggling to balance cancer treatments with insulin shots and diabetes drugs. Because cancer is generally seen as the more lethal of the two diseases, patients often make it the priority.
“Although cancer is no longer generally a death sentence, for many patients, they see it as that no matter what you say,” said Dr. June McKoy, a geriatric oncologist at the Northwestern University Feinberg School of Medicine. “Suddenly, they put their diabetes on the back burner, and they focus on the cancer.” But high blood sugar can damage kidneys and blood vessels, strain the immune system and worsen cancer prognosis.
Researchers say that the link between the two diseases is complex and driven by many factors. Typically, though, it is diabetes that sets the stage for cancer. “Most cancers don’t cause diabetes,” said Dr. Pankaj Shah, an endocrinologist at the Mayo Clinic in Rochester, Minn. “Mostly diabetes increases the risk of cancer.”
Type 2 diabetes is often preceded by chronically high insulin levels and high blood sugar, fertile conditions for cancer. Insulin is known to fuel cell growth, and cancer cells consume glucose out of proportion to other nutrients. The two diseases share many risk factors as well, including obesity, poor diet, physical inactivity, smoking and advanced age.
Another factor that complicates the relationship are the treatments given to patients. Diabetes drugs can have an impact on cancer prognosis and vice versa. Type 2 diabetics treated with the drug metformin, for example, develop cancer less frequently than diabetics given other medications. A number of clinical trials are now under way to see how well the drug performs as a cancer treatment.
Drugs used against cancer, on the other hand, tend to worsen diabetes. Chemotherapy can wreak havoc on blood sugar levels, and glucocorticoids, which are widely prescribed to alleviate nausea in cancer patients, promote insulin resistance, said Dr. Lorraine L. Lipscombe of Women’s College Hospital in Toronto.
Dr. Lipscombe was the lead author of a large study last month that found that breast cancer survivors were 20 percent more likely to receive a diabetes diagnosis than other women. The study found evidence that glucocorticoids and chemotherapy may hasten the onset of diabetes.
“They don’t cause diabetes in everyone, but they can bring out or unmask it in people who might already be vulnerable,” she said.
For diabetics who are used to tightly monitoring their blood sugar levels, the impact of cancer drugs can be alarming. Rigoberto Cortes, 71, a former metal worker in Chicago, has had Type 2 diabetes for over two decades. A year ago, he was told he had Stage 3 colon cancer.
“When I started chemotherapy, my sugar level was going way up and way down like never before,” he said. “I kept asking my oncologist what I should do.”
Mr. Cortes said his oncologist was not very concerned by the blood sugar swings. He eventually got a second opinion and switched doctors. He also lost weight and changed his eating habits, which helped minimize his blood sugar swings.
Although every case is different, the general strategy in treating such patients should be to get the cancer under control first, said Dr. Shah at the Mayo Clinic.
“Diabetes treatment essentially is given to prevent long-term complications,” he added.
At some hospitals, oncologists may take responsibility for managing blood sugar and other diabetes concerns in their cancer patients. But ideally, treatments should be coordinated by a team that includes a certified diabetes educator.
“They go over diet with the patient, review their medication, review their insulin,” said Dr. McKoy of Northwestern. “They can play a big role.”
For a diabetic trying to navigate the world of cancer, or a cancer patient navigating the world of diabetes, such interventions can be crucial. In a study published in October, Dr. McKoy and her colleagues looked at several years of health records for over 200,000 people with Type II diabetes who developed cancer.
Those who underwent a diabetes counseling session after their cancer diagnosis — consisting of two sessions a week for four to six weeks — were more likely to receives tests of hemoglobin A1c levels, a barometer of how well blood sugar has been controlled over time, and to take care of their blood sugar levels. As a result, they had fewer emergency room visits, fewer hospital admissions and lower health care costs.
Ms. Gray, the former schoolteacher in Durham, learned this firsthand. After her recent emergency, she worked with a diabetes educator at Duke University Hospital. Ms. Gray learned tips and strategies to balance the two diseases, including ways to keep her blood sugar normal when cancer treatments ruin her appetite.
“I came into the hospital and they got me back on track,” she said. “I was just so focused on the cancer. It changed everything. But I’ve learned how to face this.”
