In this study of assessment of breast cancer mortality rates from 2000 to 2017 in women from São Paulo, Brazil, it was observed that, while in white women the rates tend to a reduction, in black women the rates tend to increase. The same trends were observed in cancer mortality rates in general. The woman's age in the year of death did not influence this result, as the qualification of death records and the reduction in deaths due to external or violent causes.
The reduction in breast cancer mortality is the result of improved access to early diagnosis and timely treatment. The therapeutic evolution, especially the development of new drugs and specific therapies, is considered the main factor that has had an impact on breast cancer mortality in recent decades [8, 19]. Trastuzumab, for example, is available at the universal health care system since 2013 in São Paulo state, so women carrying the HER2/neu protein would have a better prognosis since them .
However, inequity in access to therapeutic modalities can influence population rates in different ways. The trend observed in the reduction of mortality in white women as opposed to the increase in rates in black women indicates the clear influence of race on this issue in the Brazilian population.
The incidence rates of breast cancer are increasing in Brazil and worldwide . Therefore, without adequate intervention, mortality rates are also expected to increase. The increase in mortality rates among black women may reflect delay in diagnosis, difficulty in accessing highly complex services for treatment or biological variations. In North America women, rates in black women are 21% lower for hormonal receptor (HR) and HER2 positive, 29% higher in HR negative and HER2 positive, and 93% higher for triple-negative subtypes . This data may justify the rough differences observed among race, but not the opposite trends observed in the study.
The increase in cancer mortality rates in general observed in this study suggests that access to treatment should be the main factor that influenced these results. Delays in surgical treatment due to race are reported in the USA . Also, racial minorities are more likely to receive more non-standardized treatments (out of standard protocols), such as less indication for surgical treatment, fewer sentinel lymph node biopsies and reconstructions, and less access to adjuvant treatment [21–24]. Regarding chemotherapy and hormone therapy, there is a greater chance of delaying its onset, which can lead to significant differences in survival [21, 25]. In Brazil, greater delays have been reported in populations with lower income, less education and non-white ethnic groups .
A possible explanation for these pieces of evidence is that the race factor is being influenced by socio-economic variables. However, it is necessary to consider a possible implicit bias in the health professional behaviour, when a difference in the preference for a given social group would negatively impact communication, clinical investigation and decision in the treatment of vulnerable patients . In Brazil, an assessment of satisfaction with health care and hospitalization observed 12.2% of non-satisfied among white patients and 17.4% among blacks and browns patients . The probability of a black or brown person looking for a health service and not being seen is twice as high as a white person .
In general, international literature does not support the hypothesis of a biological plausibility that would justify these observed differences. A population-based study in the USA showed that the black population is twice as susceptible to death than the white population in tumours that express hormone receptors, with no difference between the triple-negative types . Another study points out that despite hormonal subtype, socioeconomic status or access to health services, racial disparities in diagnosis, treatment and survival still persist .
The incidence of hormone receptor-negative tumours is higher in black than in white women [23, 28, 29]. Certain genetic factors may be associated with this fact, such as more frequent mutations in BRCA and other, although the real functional impact of these on the incidence and progression of triple-negative cancers in this population is still unknown . In the specific case of tumours with negative hormone receptors, it is known that the delay in diagnosis and referral can compromise the effectiveness of the treatment .
In this study, data on stage and molecular subtypes were not available. It is known that more aggressive tumours tend to affect younger populations [30, 31]. In the group of women aged 40 to 49, mortality decreased significantly among white women and increased significantly among black women. It is not possible to determine whether tumours in black women were more aggressive than those in white women, but this data also reinforces the hypothesis of less access to treatment faced by black women. Survival studies can elucidate this issue.
The hypothesis that mortality rates may have been influenced by an improvement in the quality of filling out death certificates among black women in the period was investigated. The analysis of mortality rates due to ill-defined causes revealed that the tendency towards reduction was observed for both white and black women, with a more important fall among white women, which could have influenced the results in an inverse way to the hypothesis made. Another interesting fact is that in the period, there was a significant reduction in mortality from external causes in the population in general, more significant among white women, which should not have influenced the results either.
This is a population-based study in a region that concentrates about 1/5 of the Brazillian population, being quite representative of other large urban centres in middle-income countries. It is also important to note that the data from the death registry information system in the State of São Paulo are of high quality, considered as the best in the country. In this way, we consider that this is the best information that might be obtained for the analyzes to be carried out. The main limitations of the study are the lack of data on the stage and molecular subtypes of breast cancers. We believe that future survival analyzes from population-based cancer registries can support the evidence generated in this study.