Women with diabetes are at a greater risk of being diagnosed with advanced-stage breast cancer, according to a retrospective study published in Breast Cancer Research and Treatment.
Women with diabetes were 14% more likely to present with stage II breast cancer, 21% more likely to present with stage III breast cancer, and 16% more likely to present with stage IV breast cancer than they were with stage I breast cancer.
The results found that breast cancer patients with diabetes had a nearly 15% decrease in 5-year survival rate compared with those without diabetes.
The study, by the Institute for Clinical Evaluative Sciences and Women’s College Hospital, analyzed data on 38,407 women who were newly diagnosed with breast cancer between 2007 and 2012 in Ontario, Canada.
"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 Lorraine Lipscombe, MD, an associate professor in the department of medicine at the University of Toronto and a researcher at the Institute for Clinical Evaluative Sciences and Women’s College Research Institute, in a statement.
Of the women included in the analysis, 15.9% (6,115 women) had diabetes.
Patients with diabetes tended to be older, have higher comorbidities, and had more primary care physician visits 2 years before their cancer diagnosis. These women were also more likely to live in lower income neighborhoods.
A total of 41.2% of the patients studied were diagnosed with stage I breast cancer; 39.2% with stage II; 14.5% with stage III; and 5.1% with stage IV.
Prior studies have suggested that diabetics may have both a higher risk of developing cancer and higher mortality from their cancer. While patients with diabetes may not be treated as aggressively due to comorbidities, contributing to a greater cancer mortality rate, the authors of the current study wanted to investigate whether cancer diagnosis at a more advanced stage could also play a part.
The study found that women with diabetes had lower rates of annual mammography in the 3 years before their cancer diagnosis. However, the association between diagnosis at a more advanced breast cancer stage and diabetes persisted even among women who did receive consistent mammography screening.
Women with diabetes had a 16% higher risk of lymph node metastases and were 16% more likely to have tumors greater than 2 cm.
“These findings suggest that diabetes may predispose women to more rapidly progressive breast cancers, leading to more advanced-stage disease at diagnosis even if they receive regular screening mammograms,” the study authors wrote. The authors suggested that diabetes may result in decreased sensitivity of mammography due to the association of type II diabetes with obesity.
“While further studies are needed to evaluate the impact of these findings, breast cancer screening and detection practices may need to be modified in patients with diabetes,” concluded the authors.