Researchers know that diabetes can coexist with cancer; requiring both diabetes management and cancer treatments. But a large Canada study found that 20% of women with postmenopausal breast cancer would be at high risk for Type 2 diabetes.
Insulin resistance has been linked to an increased risk of breast cancer and is also characteristic of type 2 diabetes, states Diabeties Journals. The same was found by Ontario doctors in a CBC article.
Knowing that women with diabetes have a higher risk of postmenopausal breast cancer than those without diabetes, researchers had set out to explore the reverse: are breast cancer survivors more likely to develop diabetes?
Two things resulted from the Canada diabetes study:
(1) It was found that post-menopausal survivors of breast cancer are more likely to develop diabetes than controls without breast cancer.
(2) It was found that the relationship between breast cancer and diabetes varies depending on whether a breast cancer survivor has undergone chemotherapy - making the increased diabetes risk differing with chemotherapy.
Additional factors are that cancer risk occurs much earlier than diabetes in insulin-resistant individuals, when insulin levels are high. Insulin resistance is connected with high insulin levels; and there is evidence that high-circulating insulin may increase the risk of cancer. The results showed that one in 10 women developed diabetes over the study period.
Dr. Lorraine Lipscombe and colleagues from the Women's College Hospital, Women's College Research Institute, in Toronto, ON, Canada, used population-based data from the area. A 1996 to 2008 study of diabetic women aged 55 plus with breast cancer were compared to age-matched women without breast cancer. The study looked further at whether or not the women with breast cancer had undergone chemotherapy.
Of the 24,976 breast cancer survivors and 124,880 controls, 9.7% of the population would develop diabetes over a mean follow-up of 5.8 years. Two years after the breast cancer diagnosis, the risk of diabetes among breast cancer survivors compared with women without breast cancer began to show a 7% increased risk that rose to 21% after 10 years.
However, the 4,404 women with breast cancer who received adjuvant chemotherapy showed the opposite relationship: risk was highest in the first two years after diagnosis (a 24% increased risk compared with controls) and then declined to an 8% increased risk after 10 years, according to Dr. Lorraine Lipscombe.
"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. Oestrogen 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."