An article published this week in the new edition of the journal Breast Cancer Research and Treatment examined the impact of diabetes on the stage of breast cancer diagnosis. The study entitled, “The association between diabetes and breast cancer stage at diagnosis: A population-based study” concluded that a diagnosis of diabetes is associated with advanced stages breast 
cancer in patients and could contribute to the higher mortality rates.
Background terminology:
- Confounder variable: occurs when the observed result between exposure and disease differs from the truth because of the influence of the third variable (confounding variable).
About the Study:
In this study, researchers evaluated the records of over 38,000 Ontario women aged 20 to 105 years who were newly diagnosed with invasive breast cancer between January 1, 2007 and December 31, 2012. They compared stage (I, II, III, or IV) at diagnosis between breast cancer patients with diabetes and those without diabetes.
The main study finding was that breast cancer patients with diabetes were significantly more likely to be diagnosed at a later stage than patients without diabetes. Other findings included:
- Women with diabetes were 14% more likely to present with Stage II breast cancer.
- Women with diabetes were 21% more likely to present with Stage III breast cancer.
- Women with diabetes were 16% more likely to present with Stage IV breast cancer.
- Women with diabetes also had a higher risk of lymph node metastases (spreading of the cancer).
- Women with diabetes also had a higher risk of developing larger tumors than women without diabetes.
- Women with diabetes were older
- Women with diabetes were less likely to have a screening mammogram within the prior 3 years.
- Women with diabetes were more likely to live in a lower income neighborhood.
In a press release about the findings, Dr. Lorraine Lipscombe, MD, MSc, Director at the Centre for Integrated Diabetes Care at Women’s College Hospital in Toronto and lead study author stated, “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. In addition, the risk of advanced stage breast cancer was greatest in younger women and those with longer-standing diabetes.”
One limitation of this study is that the researchers did not look at the possibility that race/ethnicity could be a possible confounder. There have been numerous studies showing that African-American women in particular are prone to being diagnosed with both diabetes and later stage breast cancers. Future studies should take this into account during data analysis to ensure that the difference is not an artifact of race/ethnicity.
