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.
Institute for Clinical Evaluative Sciences, Toronto, Ontario, Canada. Lorraine.Lipscombe@ices.on.ca
Lorraine L
LL
Lipscombe
Pamela J
PJ
Goodwin
Bernard
B
Zinman
John R
JR
McLaughlin
Janet E
JE
Hux
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