Link Between Pancreatic Cancer & Diabetes Not Fully Understood

Link Between Pancreatic Cancer and Diabetes Not Fully Understood

Suresh Chari, M.D.

DEAR MAYO CLINIC:

Does having diabetes increase the chance of pancreatic cancer?

Would a test at the time diabetes is diagnosed help in the early detection of pancreatic cancer? Does going from diabetes pills to insulin increase the chance of getting pancreatic cancer?

ANSWER:

Considerable research has been done to examine the complex relationship between pancreatic cancer and diabetes.

While long-standing diabetes may slightly increase the risk of pancreatic cancer, new-onset diabetes is more likely to signal the presence of underlying cancer. However, distinguishing those who have pancreatic cancer-induced diabetes from the more common type 2 diabetes is a significant challenge. Complicating the issue further are results of recent studies suggesting that certain treatments for diabetes may decrease or increase the risk of pancreatic cancer.

Your pancreas makes insulin, a hormone that regulates blood sugar levels. Diabetes is a state in which blood sugar levels are high. Diabetes develops when your pancreas produces little or no insulin or when your body becomes resistant to insulin.

Studies focusing on people with long-standing diabetes (five or more years) have found that their risk for pancreatic cancer is slightly elevated. This phenomenon has been of interest to scientists who are trying to understand why some people get pancreatic cancer. However, since pancreatic cancer is rare, this small increase doesn't represent a significant health risk, nor does it call for increased cancer screening of patients with long-standing diabetes.

On the other hand, new development of diabetes after age 50 may be a harbinger of pancreatic cancer. Recently, Mayo Clinic researchers studied people who developed diabetes after age 50. They examined the participants' medical records to determine when their blood sugar levels were elevated to the point of becoming diabetic. Then, they reviewed the medical records for three years thereafter. The rate of pancreatic cancer in the study group was eight times higher than in the general population.

The researchers theorize that in some people who developed pancreatic cancer within this group, diabetes was actually caused by the cancer. They believe that pancreatic cancer reduced the pancreas' ability to produce insulin, resulting in diabetes.

While these results may seem to call for everyone diagnosed with diabetes after age 50 to be screened for pancreatic cancer, it isn't that easy. There is no simple screening test for pancreatic cancer. No blood test exists to determine if a person has pancreatic cancer, and imaging tests -- such as computerized tomography (CT) scans -- can't reliably detect pancreatic cancer in its early stages.

The search for a marker that could be detected by a blood test and distinguish between diabetes caused by pancreatic cancer and other forms of diabetes is an important area of research. If such a marker could be found, some cases of pancreatic cancer could be diagnosed in the early stages of the disease and treatment started promptly, when it's most effective.

One test that can reliably detect pancreatic cancer, endoscopic ultrasonography, is an invasive and expensive procedure. Many insurance companies won't cover the cost of this study based on a diabetes diagnosis alone. In addition, having large numbers of people undergo this type of invasive test isn't feasible in many medical centers.

Further complicating matters, people who develop diabetes as a result of pancreatic cancer usually have diabetic symptoms similar to individuals who develop diabetes for other reasons. But prior to the onset of cancer symptoms, there does seem to be one subtle clue that may hint at a difference.

People who develop diabetes because of pancreatic cancer tend to experience unexplained weight loss at the onset of diabetes.

Those who have type 2 diabetes often gain weight. So, endoscopic ultrasonography or other testing for pancreatic cancer does seem appropriate for patients diagnosed after age 50 who experience weight loss after developing diabetes.

Recently, diabetes treatment has also come under scrutiny for a possible link to cancer.

These studies have examined the risk of pancreatic cancer in diabetic individuals taking specific anti-diabetic medications. One study conducted in Germany concluded that a newer form of insulin (glargine) may increase cancer risk, but that other forms -- including human insulin and other new insulins (aspart and lispro) -- do not.

However, the study didn't take into account the fact that pancreatic cancer is more common shortly after a diagnosis of diabetes.

Other recent studies suggest that subjects on the oral antidiabetic drug metformin were less likely to develop pancreatic cancer. These findings are intriguing, as metformin is known to inhibit cancer growth in the laboratory. More research is necessary to determine what, if anything, the findings mean for the treatment of diabetic patients.

As you can see, there are many more questions than answers regarding the connection between diabetes and pancreatic cancer. A significant amount of research is ongoing. If you're a diabetic patient concerned about your risk of cancer, talk to your doctor. And remember, never discontinue treatment or change medication without consulting your doctor first.

-- Suresh Chari, M.D., Gastroenterology, Mayo Clinic, Rochester, Minn.

Medical Edge from Mayo Clinic is an educational resource and doesn't replace regular medical care.

More HEALTH & WELLNESS ...