The findings, published in the journal Breast Cancer Research and Treatment, confirm a strong link between diabetes and later stage breast cancer at diagnosis for Canadian women.
“Our findings suggest that women with diabetes may be predisposed to more advanced stage breast cancer, which may be a contributor to their higher cancer mortality,” said Dr. Lorraine Lipscombe, a scientist at ICES and Women’s College Research Institute.
In the study, Dr. Lipscombe examined stage at diagnosis among women aged 20-105 years who were newly diagnosed with invasive breast cancer between 2007 and 2012.
From an analysis of more than 38,000 women with breast cancer, 6,115 (15.9 per cent) of the women had diabetes. Breast cancer patients with diabetes were significantly more likely to present with advanced stage breast cancer than those without diabetes. Women with diabetes were 14 per cent more likely to present with Stage II breast cancer, 21 per cent more likely to present with Stage III breast cancer, and 16 per cent more likely to present with Stage IV than to present with Stage I. The results also show lower mammogram rates in women with diabetes, which could account for later stage disease. Women with diabetes also had a higher risk of lymph node metastases (spreading of the cancer) and larger tumors than women without diabetes.
“In addition, the risk of advanced stage breast cancer was greatest in younger women and those with longer-standing diabetes,” added Lipscombe.
The study showed that the majority of diabetes patients presented with Stage II or III breast cancer, which translated into a 15 per cent decrease in five-year survival for diabetes patients at the time of cancer diagnosis.
The researchers suggest that breast cancer screening and detection practices may need to be modified in patients with diabetes to reduce the chances of later-stage detection.