Keeping Diabetes under Control Is Critical to Good Outcomes for Patients Who Also Have Cancer 

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Patients with a comorbid illness are grappling with two important diseases, and if they don’t get that refresher to remind them that [diabetes] is as critical as [cancer], they are going to ignore the diabetes.

—June McKoy, MD, MPH, JD, MBA

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Cancer and diabetes can be comorbid diseases, but often they are not comanaged. Patients may “put their diabetes on the back burner” and focus on what they perceive as the most immediate and lethal threat of cancer, according to June M. McKoy, MD, MPH, JD, MBA, Director of Geriatric Oncology for Robert H. Lurie Comprehensive Cancer Center and Associate Professor of Medicine at Northwestern University Feinberg School of Medicine in Chicago. Patients with cancer need to know “that keeping their diabetes under control is critical to a good outcome on both fronts,” Dr. McKoy told The ASCO Post.

“Patients also need to be educated that cancer is not the killer that some people think it is,” Dr. McKoy said. “We have so many survivors of cancer, but especially older persons still labor under the belief that cancer is very bad, and once you say the word cancer, their lives stop right at that second. It takes a while for them to refocus, but even when they refocus, if you do not start educating them, patients just don’t do that well.”

Education Underutilized

Dr. McKoy was recently interviewed for an article in The New York Times1 about a study looking at the effects of diabetes education on individuals with diabetes-cancer comorbidity.

“Individuals who received diabetes education were more likely to have regular outpatient follow-up (HbA1c testing), which resulted in fewer hospitalizations, lower health-care expenditures, and fewer [emergency department] visits,” according to the study, published by Population Health Management.2 Dr. McKoy, supported by a grant from the National Institutes of Health/National Cancer Institute, was the senior author of that study, and Lauren Irizarry, a 4th-year medical student working with Dr. McKoy and supported by the Northwestern University Feinberg Medical Student Summer Research Program, was the lead author.

Despite the potential benefits of diabetes education, it is often underutilized. In the study described above, which included members of commercial and Medicare Advantage health plans from a private national database of payer data, only 3.5% of individuals with diabetes-cancer comorbidity participated in diabetes education.

The Cancer-Diabetes Connection

“Cancer and diabetes are diagnosed within the same individual more frequently than would be expected by chance, even after adjusting for age,” according to a consensus report of experts jointly assembled by the American Cancer Society and the American Diabetes Association and published in Diabetes Care.3 The report cites evidence suggesting that people with diabetes have a significantly higher risk of developing some forms of cancer, particularly cancers of the liver, pancreas, and endometrium, and to a lesser degree of the colon and rectum, breast, and bladder. “Results of some, but not all, epidemiological studies suggest that diabetes may significantly increase mortality in patients with cancer,” according to the consensus report.

“Diabetes itself causes certain changes at the cellular level that we believe actually makes one prone to cancer,” Dr. McKoy said. “Oftentimes diabetes is a precursor to pancreatic cancer, and since pancreatic cancer is more common in older persons (the majority of cases being diagnosed between ages 65 and 79), for select older patients with no family history of cancer who present with diabetes, I often will do a screening ultrasound of the pancreas to make sure that they have no existing mass. Nevertheless, I am not advocating routine ultrasound screening for pancreatic cancer in ­asymptomatic persons.”

Concern about Chemotherapy

Oncologists and their patients should be aware of the effects of some chemotherapy agents on diabetes. “I think it is a major concern because chemotherapy is toxic by its very nature,” Dr. McKoy said. “One of the side effects of many of these toxic therapies is that they can affect the kidney. Carboplatin can cause kidney damage,” she said. “A very popular, very good drug for diabetes is metformin, which is metabolized through the kidney,” Dr. McKoy noted. “So you have two drugs competing, going through the kidney, and you can have further kidney damage to patients. That is certainly a problem,” Dr. McKoy said.

“Carboplatin is a drug commonly used for ovarian and lung cancers,” she continued. “Carboplatin causes so much renal toxicity and one has to be careful, especially in older populations, how it is dosed. Older people tend to have decreased lean muscle mass, and if you dose it using creatinine, you’re going to overdose a patient, so you have to dose it using creatinine clearance. But I think oncologists today are doing a much better job with how they dose carboplatin.”

Cancer and diabetes drugs can also “compete for metabolic space” in the liver, leading to serious liver problems, Dr. McKoy said.

“Doxorubicin is cardiotoxic,” she noted. “So patients with diabetes—which affects the vascular system, including the heart, so terribly—who don’t keep their diabetes under control are not going to have a heart that is strong enough to endure treatment with a drug like doxorubicin.”

Steroids can also cause problems. High-dose dexamethasone for patients with brain cancer and premedication with prednisone for patients receiving chemotherapy can “send blood sugar levels through the roof if somebody isn’t keeping an eye on that,” Dr. McKoy said. She noted that she did not know of any diabetes drugs that interfere with cancer treatment.

Who Is Watching Out for the Diabetes?

“When a patient gets cancer, the oncologist becomes the perceived primary care doctor,” Dr. McKoy said. “Patients will spend most of their time in the cancer clinic seeing an oncologist or an advanced practice nurse whose specialty is oncology. They rarely will see their primary care doctor. The oncologist is extremely busy. Who is watching out for the diabetes? You can see where we need someone else to step in.”

At Northwestern, that person is a certified diabetes educator. “If you educate patients, they know what to look for,” Dr. McKoy said. “Diabetes should be seen as a self-management disease. Patients should be trained to manage their own diabetes. The doctor is just a facilitator. Patients need to know how and when to check their sugars, and when to call in when something isn’t right. They need to know how to regulate their diet.”

For patients who have diabetes and then get cancer, Dr. McKoy refers them to a refresher course. It may have been 1, 2, or even 10 years since the patient was first diagnosed with diabetes and seen by a diabetes educator.

“The oncologist who diagnoses them or even the primary care doctor often does not send them back for diabetes education,” Dr. McKoy said. “But I do. Patients with a comorbid illness are grappling with two important diseases, and if they don’t get that refresher to remind them that this one is as critical as the one that you have just been told about, they are going to ignore the diabetes.”

Double-front Approach

Like other patients with diabetes, those who also have cancer are referred to a dietitian for help with diet modifications. “What our dietitians do is a double-front approach. They are helping patients modify their diet not only to keep their sugars controlled, but also to boost their immune system to fight this cancer,” Dr. McKoy said.

“One thing that many people never talk about is the fact that diabetes does suppress the immune system, so patients with diabetes are prone to getting certain infections, like pneumococcal pneumonias, and that is why we always give patients with diabetes the pneumococcal vaccine. So you have two suppressive actions going on—one with cancer, one with diabetes,” Dr. McKoy stated.

“We try to let our patients know that while they are not feeling anything with their diabetes, it is slowly destroying their bodies, and they need to really fight to survive both the diabetes and the new-onset cancer,” Dr. McKoy said. “I have seen the light bulb go off when you tell them that diabetes is a silent killer and that cancer can often be cured or turned into a chronic disease with which you can live for a long, long time. We tell them, “Don’t give up; you can do this. We are here. We are partnering with you. Call us.” You can see the relief on patients’ faces, and they tend to do well.” ■

Disclosure: Dr. McKoy reported no potential conflicts of interest.


1. O’Connor A: Juggling diabetes and cancer. New York Times, December 31, 2012.

2. Irizarry L, Li QE, Duncan I: Effects of Cancer Comorbidity on Disease Management: Making the Case for Diabetes Education (A Report from the SOAR Program). Population Health Management. October 31, 2012 (early release online).

3. Giovannucci E, Harlan DM, Archer MC: Diabetes and cancer: A consensus report. Diabetes Care 33:1674-1685, 2010.

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