Socioeconomic status and prostate cancer incidence and mortality rates among the diverse population of California

Black men are more likely to be diagnosed with prostate cancer compared to White men and are two to four times more likely to die from the disease than other racial and ethnic groups. (Source: ISTOCK, FATCAMERA)

Prostate cancer is a leading cause of cancer morbidity and mortality among men in the US, with an estimated 186,320 new cases and 28,660 deaths in 2008. The disease exhibits significant racial and ethnic disparities in incidence and mortality rates, with African-Americans facing the highest burden, followed by non-Hispanic Whites, Hispanics , and Asian/Pacific Islanders . The reasons for these disparities are not well understood and likely involve a combination of social, environmental, and genetic factors. To understand the interaction of these factors, it is essential to evaluate the relative contribution of each domain to the disparity in prostate cancer rates.

Socioeconomic status (SES) is linked to various factors that may collectively influence the burden of prostate cancer, such as lifestyle, environmental risk factors, and access to healthcare services. Following the adoption of prostate-specific antigen (PSA) screening, most studies have reported associations between higher SES and increased prostate cancer incidence. However, these associations vary across different racial and ethnic groups. For example, a large national study found higher SES associated with increased incidence among non-Hispanic Whites but not among Hispanics or African-Americans. Conversely, a study in the San Francisco Bay Area found a positive relationship between SES and prostate cancer incidence among Asian/Pacific Islanders and Hispanics, but not among non-Hispanic Whites and African-Americans. However, higher SES is generally associated with lower prostate cancer mortality rates.

The extent to which SES accounts for the substantial racial and ethnic disparities in prostate cancer incidence and mortality among men in the US is not well understood. Previous studies have primarily focused on differences between African-Americans and Whites, often excluding other racial and ethnic groups. These studies generally agree that SES does not fully explain racial and ethnic differences in prostate cancer incidence. However, findings are mixed regarding the contribution of SES to survival differences between racial and ethnic groups.

To further clarify the relationship between SES, race/ethnicity, and prostate cancer incidence and mortality, we studied a population-based series of prostate cancer patients, including a large number of African-Americans, non-Hispanic Whites, Hispanics, and Asian/Pacific Islanders, for whom small area-level SES information was available.

Materials and Methods

Prostate Cancer Patients

We obtained data from the California Cancer Registry (CCR) , which includes three of the National Cancer Institute’s Surveillance, Epidemiology, and End Results (SEER) program registries. The data covered 102,691 incident cases of invasive prostate cancer and 9,029 prostate cancer deaths for two periods: January 1, 1998 to December 31, 2002, and January 1, 1999 to December 31, 2001. Information on patient age at diagnosis, race/ethnicity, residential address, and tumor stage and grade was abstracted from medical records. Information on prostate cancer deaths, including age, race/ethnicity, and residential address, was obtained from death certificates. Race/ethnicity was classified into African-American, Asian/Pacific Islander, Hispanic (of any race), non-Hispanic White, and other/unknown. Nonaggressive disease was defined as tumors confined to the prostate and well or moderately differentiated, while aggressive disease included regional and distant tumors or localized tumors that were poorly differentiated or undifferentiated.

We restricted the study to men aged 45 years and older at diagnosis or death due to prostate cancer, excluding those with unknown race/ethnicity, resulting in a final population of 98,484 incident prostate cancer cases and 8,997 prostate cancer deaths.

Socioeconomic Status and Population Data

Individual-level SES characteristics are not routinely collected by most US cancer registries, including the CCR. However, residential address at diagnosis is routinely geocoded by the CCR, and address at death was obtained from California death certificate files. Residential addresses were linked to neighborhood-level SES characteristics from the US Census Bureau . Census block groups were used as the smallest geographic units for which both SES characteristics and population counts were available. Patients with unknown block groups were randomly allocated to block groups within the same county.

A previously developed method was used to assign a single measure of SES to each California census block group for the study periods. Principal component analysis was used to develop a single SES index from seven census-based SES indicators: mean years of education, median household income, percent living 200% below poverty level, percent blue-collar workers, percent older than 16 years in the workforce without a job, median rent, and median house value. This index incorporates education, income, and occupation and was used to assign a standardized score to each block group, categorized into quintiles.

Statistical Analysis

Case counts and population estimates were stratified by 10-year age groups, race/ethnicity, and neighborhood SES quintile. Prostate cancer incidence and mortality rates were calculated per 100,000 individuals. SES quintile-specific incidence and mortality rate ratios (RR) and 95% confidence intervals (CI) were estimated and age-adjusted to the 2000 US standard population using SEERStat, version 6.3.4.

Results

Socioeconomic Status and Prostate Cancer Incidence

For 98,484 incident cases of prostate cancer, the distribution of race/ethnicity, stage, grade, and neighborhood SES quintile varied by age group. Non-Hispanic Whites represented over 68% of all cases across all age groups. African-Americans were the second largest group among the youngest age group (45–54 years) but the smallest among the oldest (85+ years). Hispanics and Asian/Pacific Islanders represented 10–14% and 4–7% of the cases, respectively. Most cases were of nonaggressive, localized disease, and moderately differentiated.

Higher SES was associated with increased prostate cancer incidence across all racial and ethnic groups. Those in the highest SES quintile had a 28% higher incidence rate than those in the lowest quintile. The largest difference was observed among Hispanics, with an 80% higher incidence rate in the highest SES quintile compared to the lowest. This pattern was consistent for both nonaggressive and aggressive disease, with higher SES associated with significantly higher prostate cancer rates.

For African-Americans and non-Hispanic Whites, prostate cancer incidence peaked at ages 65–74, while for Hispanics and Asian/Pacific Islanders, it peaked at ages 75–84. African-Americans had the highest incidence rates among younger men aged 45–64 years, regardless of SES. Among older men aged 75–84 years, Hispanics had the second highest incidence rates, following African-Americans. For aggressive prostate cancer, incidence rates were highest for African-Americans in all age groups and were two to three times higher than for non-Hispanic Whites among men aged 45–64 years.

Socioeconomic Status and Prostate Cancer Mortality

Non-Hispanic Whites comprised the majority of the 8,997 prostate cancer deaths across all age groups. SES and prostate cancer mortality rates were inversely associated, with higher SES linked to lower mortality rates. Men in the highest SES quintile had a 12% lower risk of prostate cancer death compared to those in the lowest quintile. Although there were no significant differences in mortality rates across SES levels within each racial/ethnic group, non-Hispanic Whites showed a trend of lower mortality rates with higher SES.

African-Americans had the highest mortality rates across all SES quintiles, with rates two to five times higher than those of non-Hispanic Whites. Asian/Pacific Islanders had the lowest mortality rates, generally less than half that of non-Hispanic Whites. Hispanics had slightly lower mortality rates than non-Hispanic Whites in most age and SES groups.

In summary, socioeconomic status alone does not fully account for the differences in prostate cancer burden among African-Americans, non-Hispanic Whites, Hispanics, and Asian/Pacific Islanders. Large multiethnic studies with individual- and area-level SES measures are needed to corroborate these findings. Understanding the complexities of racial and ethnic differences in screening, treatment, biological, and environmental factors will aid in developing targeted interventions to reduce social inequalities in prostate cancer incidence and mortality. Source: NCBI