Survivors of breast cancer, who are post-menopausal, have a higher chance of developing diabetes. Scientists are becoming increasingly aware of an association between diabetes and cancer. In this article, we discuss the link.
A study, published in Diabetologia, is the largest to observe the link between surviving breast cancer and eventually developing diabetes; it also showed that whether the patient went on to develop diabetes was closely associated with having undergone chemotherapy.
The opposite interaction has also been observed: females with diabetes have a 20 percent chance of developing postmenopausal breast cancer. A study from last year demonstrated that people with diabetes over the age of 60 are more likely to develop breast cancer, compared with their counterparts without diabetes.
The connection has been made as a result of improvements in diagnosis and treatment of breast cancer. As more women survive breast cancer, it is becoming increasingly important to understand the long-term outcomes for survivors as they grow older.
However, few studies have tried to determine what the risk of developing diabetes is for a breast cancer survivor. The study in Diabetalogia is an example of the new research that has established the connection between breast cancer and diabetes more firmly.
The team, led by Dr. Lorraine Lipscombe (Women’s College Hospital, Women’s College Research Institute, Toronto, ON, Canada), gathered and analyzed data from Ontario. The goal was to compare the prevalence of diabetes among females older than 55 with breast cancer (1996-2008) to women of the same age without the disease.
Whether or not the patient had undergone chemotherapy was also determined. There were 24,976 breast cancer survivors and 124,880 controls involved in the experiment.
The results of the study showed that:
- Out of all the subjects, 9.7 percent developed diabetes over an average follow-up of 5.8 years.
- Two years after diagnosis, the risk of diabetes among breast cancer survivors grew to 7 percent, compared with the women without cancer.
- After 10 years, the 7 percent increased risk rose to 21 percent.
The 4,404 patients who received adjuvant chemotherapy showed the opposite correlation. In the first 2 years after diagnosis, their risk for diabetes was the highest (24 percent increased risk compared with the control group). But, after 10 years, the risk reduced to 8 percent.
Does chemotherapy increase the risk of diabetes in breast cancer patients?
Dr Lipscombe said:
“It is possible that chemotherapy treatment may bring out diabetes earlier in susceptible women. Increased weight gain has been noted in the setting for adjuvant chemotherapy for breast cancer, which may be a factor in the increased risk of diabetes in women receiving treatment.
Estrogen suppression as a result of chemotherapy may also promote diabetes; however this may have been less of a factor in this study where most women were already post-menopausal.”
The authors believe that other factors contributed to the link between diabetes and women who underwent chemotherapy. These include:
- Medications – the glucocorticoid drugs used in chemotherapy to treat nausea and inflammation often cause hyperglycemia, or increases in blood sugar levels.
- Increased observation – females who received chemotherapy may have been observed more closely; therefore, diabetes would have been easier to detect.
According to the scientists, the risk may have reduced in the women who received chemotherapy because they developed diabetes within the first 2 years and were no longer monitored. Another reason may be because the effects of the glucocorticoids wore off with time.
The investigators say they cannot fully understand why the breast cancer survivors had a higher diabetes risk compared with controls.
Dr Lipscombe explained:
“There is, however, evidence of an association between diabetes and cancer, which may be due to risk factors common to both conditions. One such risk factor is insulin resistance, which predisposes to both diabetes and many types of cancer.”
Dr. Lipscombe concluded that the results emphasize the importance of closer monitoring of diabetes among the survivors of breast cancer.
The association of breast cancer and diabetes has been made. However, there are several ways that the risks for both conditions can be reduced.
A study led by epidemiologist Dr. Phillipe Autier examined the association between the conditions and carried out analyses on risk. The research, published in the Journal of Oncology, states that the most effective prevention is:
- physical activity
- reducing glycemic index
The study concludes:
“An association between these two common diseases could have important implications for public health with common risk factors driving further increases in both diseases yet holding the tantalizing possibility for prevention of both.”
As a result, diet and exercise remain effective ways of reducing the risk of diabetes in breast cancer patients, and vice versa.
Although the association between breast cancer and diabetes is continuously being studied, reducing obesity and promoting physical activity reduce the likelihood of developing either condition, and many other conditions associated with obesity and a sedentary lifestyle.