Higher socioeconomic status is usually associated with better health, but the opposite is true for breast cancer patients. A Canadian study of 226,169 cases showed that women from higher income neighborhoods have higher rates of breast cancer, in all age groups and geographical regions.
Marilyn J. Borugian and colleagues at Statistics Canada classified the cases into five groups, or quintiles, according to the average income in their postal code. For women aged 19 to 39, those in the lowest income quintile had a 25 percent reduced risk of breast cancer compared to those in the highest quintile.
For all age groups together, women in the lowest income quintile had 15 percent fewer breast cancer diagnoses than women in the highest income quintile. Borugian considered the possibility that higher income women receive more diagnoses because of better screening with mammograms.
However, a previous study quoted in her paper showed that breast cancer mortality in urban Canada is 12 percent lower for women in the lowest versus the highest income quintile. Thus, differences in diagnostic rates are not sufficient to explain the large differences found in her study.
Estrogen is an established risk factor for breast cancer. Women who have fewer children have a higher lifetime exposure to natural estrogen.
Borugian collected data on lifetime childbearing rates, and found that women of lower socioeconomic status in Canada have more children as well as less breast cancer. However, childbearing rates varied more with geographic area than with income, while breast cancer rates were consistent for all geographic areas.
“Breast cancer incidence is one of the few adverse health outcomes consistently associated with higher socio-economic status,” Borogian concluded. “The association may be partly related to differences in parity and screening mammography, but other factors remain to be identified.”
Socioeconomic variations in breast cancer survival are different in the United States and Canada, according to an earlier report by Kevin M. Gorey at the University of Windsor, Ontario, Canada, and colleagues.