Social, prognostic, and therapeutic factors associated with cancer survival: a population-based study in metropolitan Detroit, Michigan.

Abstract

Previously, we studied the effect of socioeconomic status (SES) on cancer survival among adults of Toronto, Ontario and Detroit, Michigan.1 Detroiters’ survival was significantly worse among people from lower SES areas for 12 of 15 relatively common types of cancer. In contrast, no such SES-survival associations were found for 12 of 15 cancer types in Toronto Between-country analysis, which compared cases arising from Toronto and Detroit’s low-income areas, revealed a significant Toronto survival advantage for 13 of 15 most prevalent cancers. Other studies demonstrated that such Canadian advantage was maintained even with a conservative comparison of Toronto’s poor with Detroit’s near poor,2 as well as in other Canada-U.S. comparative locales.3–5 Furthermore, SES acted as an effect modifier, that is, significant country-by-SES interactions were observed. Canadian survival advantages were observed only among the ecologically defined poor (residents of low-income neighborhoods). The present study aims to advance understanding of the factors associated with such disadvantaged survival among people with cancer in the United States. Nine of 10 U.S. studies on cancer survival during the past 10 years have found a significant disadvantage with low SES.1,3,6 Survival among those of relatively high SES was found to be 49 percent greater than that of their lower status counterparts. A similar SES-cancer survival association, although of attenuated magnitude (13 percent differential), has also been observed in other developed continental European and Nordic countries, as well as Australia.7–10 Interestingly, the aggregate SES-cancer survival differential among Canadian cohorts has been found to be only 3 percent.1–5,11,12 Health care systems differences, such as the greater representation of universally accessible single-payer systems in Nordic and other European countries, and Canada, may parsimoniously account for the greatly diminished SES-cancer survival associations found in these countries compared with the United States. Studies of race and cancer survival have provided further evidence for an SES-survival association in the United States.13–16 Cumulative cancer survival among blacks was found to be approximately 43 percent less than that of whites, but this difference diminished to only 8 percent in studies that provided any adjustment for socioeconomic factors or health care access.17 This analytic picture seems straightforward, but its valid policy interpretation is complicated by a number of other known relationships. For example, in the United States, such social factors as SES and race are both highly associated with cancer prognostic and treatment factors,18–25 which themselves are highly associated with cancer survival in the United States and other countries.26–28 Moreover, the associations of social factors with tumor biology in the United States29–32 and the associations of social factors with prognosis and treatment in other countries, including Canada,33–36 have all been observed to be extremely small or nonsignificant. Separately, each of these meta-estimates seems to be most consistent with a systemic, rather than an individual biological-behavioral, account. This study aims to measure the relative weight of all these factors—social, biological, standard prognostic, and therapeutic—in predicting cancer survival among a well-defined U.S. population.