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Background
Keywords
Findings
Authors
What is already known on this subject?
What does this study add?

Background

In developed countries, women of higher socio-economic status often have higher breast cancer incidence rates, compared with women of lower socio-economic 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.

Keywords

Mammography screening, parity, Poisson regression, record linkage, small-area analysis, social class, socioeconomic factors

Findings

Incidence and mortality rates for most chronic diseases including several types of cancer are higher among people of lower socio-economic status. By contrast, for female breast cancer in developed countries, the relationship may be inverted, with women of higher socio-economic status having higher rates, even when risk factors that differ by socio-economic status such as parity, age at first birth and hormone use are taken into account. Only one earlier study examined the risk of breast cancer in relation to socio-economic status in Canada, and it focused on the effects of passive smoking. [Full Text]

Authors

Marilyn J. Borugian (1-604-675-8058; mborugian@bccrc.ca), John J. Spinelli and Zenaida Abanto are with the British Columbia Cancer Agency in Vancouver, British Columbia, V5Z 1L3. Chen Lydia Xu is at the University of Aberdeen in Scotland.  Russell Wilkins is with the Health Analysis Division at Statistics Canada, Ottawa, Ontario

What is already known on this subject?

  • Data from other countries indicate an elevated risk of breast cancer among women of higher socio-economic status.
  • Factors such as number of children even born (parity) and participation in screening mammography, which also vary by socio-economic status, may be responsible for the association.

What does this study add?

  • Across Canada over a recent 13-year period, breast cancer incidence rates were highest in the most affluent neighbourhoods, and considerably lower in all other neighbourhoods.
  • Lower parity and a higher prevalence of screening mammography may be related to the higher breast cancer incidence rates among women in the highest neighbourhood income quintile, but these factors did not fully explain the differences across income categories.