Cancer, the world's No. 2 killer, is even more lethal for people with diabetes, U.S. researchers said on Tuesday.
People with diabetes who get cancer are about 40 percent more likely to die in the years following the diagnosis than cancer patients who are not diabetics, according to research published in the Journal of the American Medical Association.
The research illustrates an alarming interaction between two common medical conditions. Cancer is forecast to replace heart disease as the world's leading killer in 2010.
Meanwhile, type 2 diabetes, the form closely linked to obesity, is becoming increasingly common in many countries. For example, the rate of new cases of diabetes soared by about 90 percent in the United States in the past decade.
The findings suggest that for diabetics who are diagnosed with cancer, it may be vitally important to do what is necessary to get their diabetes under control for the sake of improving cancer survival, the researchers said.
"We move heaven and Earth to try to drop mortality risk in cancer patients by 5 percent. This is a huge target with a 40 percent increased risk. But the big question is: what can you do about it?" Dr. Frederick Brancati of Johns Hopkins University in Baltimore said in a telephone interview.
Brancati and colleagues combined the results of 23 studies involving about 125,000 people in 10 countries including the United States, Australia and the Netherlands. The studies tracked deaths from all causes in people with cancer who had diabetes and those who did not.
Looking at some specific types of cancer, the research showed a 76 percent higher risk of death for women with cancer of the uterus and a 61 percent higher risk of death for breast cancer if they also had diabetes. For colorectal cancer, there was a 32 percent higher risk of death for diabetics.
There also were increases in mortality risk for diabetics with some other types of cancer including prostate and lung cancer, but this did not reach the level of statistical significance, the researchers said.
Diabetics, who have high blood sugar levels, also are at higher risk of heart disease, stroke, kidney damage and blindness.
The design of the study did not allow the researchers to determine exactly how diabetes makes cancer more lethal. But they cited a number of possibilities.
Diabetes may predispose a person to cancer complications, or patients and doctors may pay less attention to diabetes once cancer is diagnosed, the researchers said.
Maybe the patients are paying a price for ignoring diabetes in the immediate (cancer) treatment stage and at later points," Brancati said.
In addition, some cancer therapies — especially steroid medications used in many cancer treatments — can cause blood sugar levels to go even higher, Brancati said.