Ethnic, racial and socioeconomic disparities in breast cancer survival in two Brazilian capitals between 1996 and 2012

1

Introduction

Breast cancer is the most common malignant neoplasm and the main cause of cancer-related mortality among women worldwide. Global estimates for 2018 indicate the occurrence of 2,088,849 new cases and 684,996 deaths [1] . The clinical expressions of the disease are strongly related to biological factors and characteristics such as age at menarche, parity, age at first full-term birth, and contraceptive use and perimenopausal hormone replacement are all related to its occurrence and may reflect social and economic characteristics of the population [2] . Incidence rates have historically been higher in high-income regions such as North America and Western Europe, but 46% of deaths from breast cancer each year now occur in low- and middle-income countries [13] .

While breast cancer is more common in developed regions, its consequences are felt proportionally more in low-income areas. In Brazil, an estimated 66,280 cases occurred in 2020 [4] . It was the most frequent neoplasm in women in all the macro-regions of Brazil except the North region, where it ranked second. Although the conditions of health of the Brazilian population have improved in the past 30 years, most of the improvements have occurred in higher-income areas, accentuating regional inequalities in the distribution of disease [5] .

The association between lower socioeconomic status (SES) and cancer survival has been demonstrated for various types of tumour, in several regions of the world [6] . Breast cancer survival is lower for women in less-developed regions of the world [7] , but even for women living in high-income regions, where by international standards, survival is generally high, educational level [8] and race or skin colour [910] are associated with prognostic disparities. Few studies have addressed this association in Brazil 111213 , a country with high indices of social inequality [14] . There is, however, indirect evidence suggesting that SES impacts breast cancer survival. Non-white women, especially those living in the least developed regions of the country, tend to present with more advanced disease, with a worse prognosis 151617 . Most population data sources lack individual information on SES, and analyses of health outcomes by SES require the use of ecological indicators (such as indices of socio-economic deprivation or human development), which are attributed to individuals using the place of residence as a proxy [1819] .

In population-based studies, analyses are usually performed using relative survival techniques [20] . In these methods, the excess mortality hazard associated with a diagnosis of cancer can be determined through the relation between the survival observed among cancer patients and the survival that would have been expected in the general population, which can be obtained from population life tables of all-cause mortality by age, sex and calendar year. From the excess mortality hazard (EMH), it is possible to estimate relative survival, defined as an estimate of survival from breast cancer after correction for other causes of death (competing hazards), which increase rapidly with age [2122] .

Regional disparities are still among the most relevant public health issues in Brazil and access to screening and treatment are key factors in breast cancer prognosis [23] . Given the lack of a national, or even a macroregional, Population Based Cancer Registry in Brazil, in order to compare the influence of the socioeconomic development on cancer survival, we selected two capitals, Aracaju and Curitiba, in which the Population Based Cancer Registries achieve good quality standards of data collection and reporting. These capitals are located in regions with very different levels of socioeconomic development [24] Comparing cancer survival between these two cities could help to indicate regional inequities in breast cancer prognosis in Brazil as a whole.

Given the public health importance of breast cancer in Brazil and the growing socio-economic inequalities seen in the country in the last 10 years, as well as the lack of studies in the Brazilian literature, study of the socio-economic and ethno-racial determinants of breast cancer survival can contribute to the evidence base for cancer strategies designed to reduce inequalities in survival. In this study, we have examined the impact of socio-economic status (SES) and ethno-racial group on the excess mortality hazard and on net survival from breast cancer among women residing in Aracaju and Curitiba.