Although breast cancer survival has improved in France, it appears that women living in deprived areas are more likely to die from breast cancer. However, no study has yet examined socioeconomic inequalities in breast cancer survival in La Réunion. Our objective was to examine whether socioeconomic inequalities in breast cancer survival exist in Reunion Island and whether stage at diagnosis could partly explain these differences.
A population-based cohort study of all women on Reunion Island with primary breast cancer diagnosed between 2008 and 2016 was conducted. Each woman was assigned a deprivation index based on her area of residence at diagnosis. Net survival by deprivation group and stage at diagnosis was estimated by the non parametric Pohar Perme method. The role of stage (indirect effect) was assessed using a mediation analysis extended to the relative survival framework.
At five years, net survival was significantly lower in women living in the most deprived areas than in women living in the least deprived areas (81 % (95 % CI 77–86) and 91 % (95 % CI 89–94), respectively, p < 0.0001), and mediation analysis showed that the contribution of stage at diagnosis to these survival differences was 43 %.
Our result shows that although measures to promote earlier diagnosis are important, they would only reduce socioeconomic inequalities in breast cancer survival by 43 %. To further investigate these inequalities, future research should explore the role of unmeasured mediators, such as comorbidities and treatment received, as well as the impact of specific interventions that might address the differences in mediator distribution.
- • The role of stage at diagnosis in survival inequalities was examined using mediation analysis in relative survival framework.
- • Results revealed for the first time the existence of socioeconomic inequalities in breast cancer survival in la Réunion.
- • Study suggests that measures to promote earlier diagnosis would only reduce inequalities in breast cancer survival by half.
In France, breast cancer survival is improving , but considerable differences in survival remain between regions . These inequalities in survival within the country are significant, and particularly pronounced in the overseas departments . Breast cancer survival in Reunion Island is lower than in metropolitan France, with a 5 year net survival of 81 % and 88 % respectively after standardisation for age .
Socioeconomic status (SES) is considered one of the main factors responsible for the persistent disparities in breast cancer survival. Women living in deprived areas have poorer survival . A variety of factors are involved, related to the patient, the tumor, and the health care system ; the most reported in the literature are stage at diagnosis and treatment: women living in deprived areas are often diagnosed at an advanced stage and tend to have limited treatment options, due to the high frequency of comorbidities in this population group. However, the role of stage at diagnosis on the effects of SES in breast cancer survival is not fully explained, previous research has examined stage at diagnosis as a confounding factor , whereas stage at diagnosis may instead act as a mediator between SES and survival, as SES influences stage at diagnosis and survival, so the application of mediation analysis methods would be more appropriate in this context.
Compared to women with breast cancer in metropolitan France, women in La Réunion are younger, are likely to live in deprived areas and have more comorbidities . The effect of SES on breast cancer survival is of particular interest in the context of Reunion Island and could guide specific regional priorities for breast cancer prevention.
The objective of our study was to examine the differences in net survival in breast cancer in Reunion Island between 2008 and 2016, according to the level of deprivation and stage at diagnosis; and to investigate the contribution of stage at diagnosis as a mediator in the association between deprivation and breast cancer survival.