Increased prevalence of prior breast cancer in women with newly diagnosed diabetes.
OBJECTIVE
There is growing evidence of a link between type 2 diabetes and breast cancer, possibly through insulin resistance and/or hyperinsulinemia. Because insulin levels are at their highest prior to the development of diabetes, breast cancer risk may be even greater during the pre-diabetes period.


METHODS
In this cross-sectional study, women aged 55-79 years living in Ontario, Canada, with newly diagnosed diabetes from 1994 to 2002 were identified from a validated, population-based database (N = 82,390). Prior history of breast cancer in this group was recorded from 1964 until their diabetes diagnosis from a linkable cancer registry, and was compared to a similarly aged comparison group without diabetes (N = 411,950).


RESULTS
Prior breast cancers were identified in 3.7% of women with diabetes and in 3.1% women without diabetes (odds ratio, OR 1.22, 95% confidence interval, CI 1.17-1.27, p < 0.0001). The mean time from breast cancer diagnosis to diabetes diagnosis was 7.9 years. The likelihood of a breast cancer history remained significantly higher in women with diabetes after adjustment for age, income and physician visits (OR 1.13, 95% CI 1.09-1.18, p < 0.0001).


CONCLUSIONS
These results suggest that breast cancer risk may be increased in the pre-diabetes phase and may have implications for screening and prevention strategies. Further studies are required to better characterize the processes that link insulin resistance, diabetes and breast cancer.
Lipscombe
Lorraine L
LL
Institute for Clinical Evaluative Sciences, Toronto, Ontario, Canada. Lorraine.Lipscombe@ices.on.ca
Goodwin
Pamela J
PJ
Zinman
Bernard
B
McLaughlin
John R
JR
Hux
Janet E
JE
D000368:Aged; D001943:Breast Neoplasms / Q000150:complications* / Q000453:epidemiology*; D048909:Diabetes Complications / Q000453:epidemiology*; D003924:Diabetes Mellitus, Type 2 / Q000150:complications* / Q000453:epidemiology*; D005260:Female; D006801:Humans; D015994:Incidence; D007333:Insulin Resistance; D008875:Middle Aged; D016017:Odds Ratio; D012042:Registries