Social class is an important and independent prognostic factor of breast cancer mortality.

Reasons of the important impact of socioeconomic status on breast cancer prognosis are far from established. This study aims to evaluate and explain the social disparities in breast cancer survival in the Swiss canton of Geneva, where healthcare costs and life expectancy are among the highest in the world. This population-based study included all 3,920 female residents of Geneva, who were diagnosed with invasive breast cancer before the age of 70 years between 1980 and 2000. Patients were divided into 4 socioeconomic groups, according to the woman's last occupation. We used Cox multivariate regression analysis to identify reasons for the socioeconomic inequalities in breast cancer survival. Compared to patients of high social class, those of low social class had an increased risk (unadjusted hazard ratio [HR] 2.4, 95% CI: 1.6-3.5) of dying as a result of breast cancer. These women were more often foreigners, less frequently had screen-detected cancer and were at more advanced stage at diagnosis. They less frequently underwent breast-conserving surgery, hormonal therapy, and chemotherapy, in particular, in case of axillary lymph node involvement. When adjusting for all these factors, patients of low social class still had a significantly increased risk of dying of breast cancer (HR 1.8, 95% CI: 1.2-2.6). Overmortality linked to low SES is only partly explained by delayed diagnosis, unfavorable tumor characteristics and suboptimal treatments. Other factors, not measured in this study, also could play a role. While waiting for the outcome of other researches, we should consider socioeconomic status as an independent prognostic factor and provide intensified support and surveillance to women of low social class. Copyright 2006 Wiley-Liss, Inc.