Breast cancer incidence and neighbourhood income.

Background: In developed countries, women of higher socioeconomic status often have higher breast cancer incidence rates, compared with women of lower socioeconomic status.

Data And Methods: Data were extracted from the Canadian Cancer Registry for the 229,955 cases of adult female invasive breast cancer diagnosed from 1992 through 2004. Postal code at diagnosis was used to determine neighbourhood income quintile. Breast cancer incidence was examined by year, region, age and neighbourhood income quintile. Census data for 1991 on children ever born and British Columbia data for 2006 on first-time attendance at mammography screening were analyzed by neighbourhood income quintile.

Results: Residence in the lowest as opposed to the highest neighbourhood income quintile was associated with a 15% lower risk of being diagnosed with breast cancer. Higher income levels were associated with lower parity in 1991 and a higher prevalence of first-time screening mammography in British Columbia in 2006.

Interpretation: Canadian data support an association between the diagnosis of invasive breast cancer and neighbourhood income quintile. Parity and mammography screening may account for some differences in incidence.