Community-And Individual-Level Socioeconomic Status and Breast Cancer Risk: Multilevel Modeling on Cape Cod, Massachusetts

Article excerpt

BACKGROUND: Previous research demonstrated increased risk of breast cancer associated with higher socioeconomic status (SES) measured at both the individual and community levels. However, little attention has been paid to simultaneously examining both measures.

OBJECTIVES: We evaluated the independent influences of individual and community SES on the risk of breast cancer using case--control data. Because our previous work suggests that associations may be stronger after including a latency period, we also assessed the effect of community-level SES assuming a 10-year latency period.

METHODS: We obtained individual education for cases and matched controls diagnosed between 1987 and 1993 on Cape Cod, Massachusetts (USA). We acquired community-level SES from census data for 1980 and 1990. Using SES data at diagnosis and 10 years earlier, we constructed models for breast cancer risk using individual-level SES only, community-level SES only, and a multilevel analysis including both. We adjusted models for other individual-level risk factors.

RESULTS: Women with the highest education were at greater risk of developing breast cancer in both 1980 and 1990 [odds ratio (OR) = 1.17 and 1.19, respectively]. Similarly, women living in the highest-SES communities in 1990 had greater risk (OR = 1.30). Results were stronger in the analyses considering a latency period (OR = 1.69). Adjusting for intragroup correlation had little effect on the analyses.

CONCLUSIONS: Models including individual-or community-level measures of SES produced associations similar to those observed in previous research. Results for models including both measures are consistent with a contextual effect of SES on risk of breast cancer independent of individual SES.

KEY WORDS: breast cancer, latency, multilevel modeling, socioeconomic status. Environ Health Perspect 116: 1125-1129 (2008). doi: 10.1289/ehp.l0818 available via http://dx.doi.org/[Online 25 April 2008]

Over the course of her lifetime, approximately one woman out of every eight will develop invasive breast cancer. Breast cancer remains the most commonly diagnosed non-skin cancer and is the second leading cause of cancer death in women (American Cancer Society 2006). Because of its frequency, the causes of breast cancer have been investigated a great deal at both the individual and community levels. On an individual basis, researchers have determined that characteristics such as age, race, religion, and socioeconomic status (SES) are associated with a woman's risk of developing breast cancer (Kelsey and Horn-Ross 1993). Rates rise sharply with age and are highest among white women and Jewish women. Women of higher SES/socioeconomic position are also more likely to develop breast cancer. In particular, higher individual educational attainment, as well as higher individual income, are associated with increased risk (Heck and Pamuk 1997; Kelsey and Bernstein 1996).

Overall, community-level SES is also associated with breast cancer incidence. Similar to the results of studies that examine individual SES, higher educational attainment and income as measured at the community level are also associated with higher incidence of breast cancer (Devesa and Diamond 1980; Gorey et al. 1998; Mackillop et al. 2000; Yost et al. 2001).

Although previous research has provided much information about these separate associations, few prior studies examined individual and community SES simultaneously. As a result, it is unclear whether the greater breast cancer incidence in high-SES communities is attributable to a greater number of high-SES women living in an area--that is, the composition of the areas--or to some aspect of high-SES communities that confers a greater risk of being diagnosed to all residents, regardless of their SES, that is, a contextual effect. For example, communities with higher SES may have greater access to screening mammography and diagnose more cases of breast cancer, even if the true incidence rates are otherwise similar. …