The current study reports the incidence, deaths, and DALYs for age-standardised rates for breast cancer across 195 countries between 1990 and 2017. Globally, there was a significant increase in age-standardised incidence rates, while age-standardised death and DALY rates were found to have a declining trend. Several regions, such as south Asia, southern sub-Saharan Africa, and high-income Asia Pacific, Caribbean, central Asia, central Latin America, and eastern Europe showed different patterns with significant increase in both incidence and death age-standardised rates. Attempts were made to compare our findings with previous studies, however, no studies were available to allow a direct comparison at the country-specific level to determine the burden of breast cancer comprehensively. The closest comparator was from the Global Cancer Incidence, Mortality and Prevalence (GLOBOCAN) project. However, data is not annually updated to allow direct comparison of GBD with GLOBOCAN for the same time periods. In particular, despite availability of 2018 GLOBOCAN data no estimates have been reported for the time period 2013 to 2017. Based on available data, the GLOBOCAN 2018 estimated 2,088,849 (95% UI: 2,003,730–2,177,580) incident cases for breast cancer, which is relatively higher than our 2017 estimates (1,937,574 [95% UI: 1,868,019–2,000,363]). Likewise, GLOBOCAN 2018 estimated 626,679 (95% UI: 606,077–647,981) deaths in 2018, which is also higher than our 2017 estimates (600,728 [95% UI: 578,725–629,932]) [18]. Although the age-standardised rates reported in GLOBOCAN and GBD could not be compared due to differences in the standard population, the ranking of countries could be compared. Belgium, Luxembourg, and the Netherlands had the highest age-standardised incidence rates of breast cancer in GLOBOCAN 2018; while, in 2017, Lebanon, the Netherlands, and the UK were found to have the highest age-standardised incidence rate in our study. Age-standardised death rates were highest in Fiji, Barbados, and Somalia in GLOBOCAN 2018, while our 2017 data found Pakistan, Tonga, and the Bahamas to have the highest age-standardised death rates [18]. These differences may be attributed to different data sources and estimating methodology. However, other studies have also reported differences in breast cancer incidence and death rates for selected countries over time, across different iterations of the GLOBOCAN project, which are not comparable with our findings as their estimates are up to 2012 [4, 7, 9–12, 19, 20]. An important point is that both GLOBOCAN and GBD studies indicate that incidence rates of breast cancer were highest in developed countries, while death rates were highest in some developing countries and some of these differences between the developed and developing countries could be explained by different prevalence of aetiological factors (i.e. alcohol consumption and high body-mass index), as well as the variations in cancer prevention, screening practice, advances in diagnosis, treatment, and oncology care, and management of health resources [12].
The trend of age-standardised incidence rate is also reported in some studies across the selected countries. A study reported increasing trends of age-standardised incidence rate for breast cancer in Australia, Ireland, Japan, the Netherlands, England, Sweden, and the USA during 1980–2009 [7]. While our study found that all of the aforementioned countries had increasing trends in age-standardised incidence rate during 1990–2017, except the USA (-13% [95% UI: -17 to -9]) and the UK (-5% [95% UI: -8 to -1]), which showed significant decreasing trends in the measurement period. Another study [11] examined the trend in age-standardised incidence and death rate for some selected countries with various time intervals, mainly during 1980–2010. They reported that age-standardised incidence rate increased for the USA, Denmark, Italy, Australia, Russia, Costa Rica, and China. Again, our study identified somewhat conflicting results finding that age-standardised incidence rates increased for all of the aforementioned countries, with the exception of the USA (-13% [95% UI: -17 to -9]) between 1990 and 2017. They also reported that age-standardised death rates are decreasing for Denmark, Italy, the USA, and Australia. In contrast, Japan, Russia, the Philippines, and China experienced an increasing trend in their study period (mainly 1980–2010) [11]. The decline in breast cancer mortality among women in developed countries may be explained by a number of reasons, most notably the introduction of a screening program (mammography) and improvement in therapy [21]. Our study found that age-standardised death rates decreased for all of these countries, except for the Philippines (76% [95% UI: 43–115]), Japan (22% [95% UI: 17–28]), and Russia (11% [95% UI: 7–14]).
Besides a considerable decrease in the mortality of breast cancer in the world during the period 1990–2017, global incidence increased over the period of study. The significant differences in breast cancer burden observed between countries could be explained by different applied methodology and the varying data quality worldwide. Also, the considerable variations in breast cancer burden can be attributed to differences in prevalence of risk factors, differences in cancer prevention and treatment, and management of health resources. Therefore, it is imperative that policy makers consult multiple data sources and consider results that provide the most representative and comprehensive information available for their country. Global- or regional-level estimates of breast cancer burden may be misleading for national policy, as there are some countries that follow completely different patterns compared to their regional estimates. When making public health policy decisions, individual countries should consider trends in breast cancer burden as well as their expected levels of burden as part of informed judgments. Modifiable risk factors such as alcohol use [22], high fasting plasma glucose [23], high body mass index [24], smoking [25], second hand smoke exposure [26], and low physical activity [27], are all reported to be associated with breast cancer burden. Breast cancer incidence and mortality increase with age and have a distinctive age-specific curve, with the age group 50–54 dividing the trends of mortality into premenopausal and postmenopausal periods. According to our results, this observation could be related to, besides the hormonal milieu, exposure to all of the described risk factors which generally increased after the age of 50. Therefore, country-level health professionals could be promoting community awareness regarding prevention programs and associated risk factors through using appropriate health education plans to decrease the breast cancer burden as much as possible. Data from this study can be used to determine trends over time, benchmarking with other similar countries and regions. In addition, this evidence can be used by policy makers to determine factors contributing to country-specific differences within regions and subsequently inform a matrix of policy options that will best meet the economic, public health, political, and societal needs of the country.
Associations between the socioeconomic development level of each country and breast cancer incidence/death rate has been studied previously, in which a positive association between breast cancer incidence and a country’s development level in 2012 was reported [28]. These results should be interpreted with caution as income alone was used as the determining factor, which on its own is an inadequate indicator of a country’s level of development. In our study we used SDI to examine socioeconomic development, which more comprehensively reflects socioeconomic development because it is a composite indicator of education, income, and fertility rate. In addition to SDI, we also report breast cancer burden by HAQ, which shows the burden of breast cancer may be decreasing with successive increments of HAQ. This suggests that publicly funded interventions such as breast cancer screening and appropriate treatment services can decrease breast cancer burden. The previous studies indicate that all of the observed reductions could not be attributable to screening alone [29–31] and it need to be considered along with education, treatment and care. For example, a study in Norway found that screening itself accounted for only about a fourth of the total reduction [32]. However, some studies reported larger contribution of screening measures, up to 60%, in decreasing the breast cancer mortality rates [33, 34]. The national-level analysis found that although SDI of countries may not be associated with breast cancer age-standardised DALY rate, it is negatively associated with HAQ. Therefore, this approach allowed us to compare the observed breast cancer burden with corresponding expected levels based on SDI (in regional- and country-level) and HAQ (in country-level) for the first time across the globe.
The present study is the most comprehensive and up-to-date study to examine level and trends of incidence, mortality, and DALYs associated with breast cancer during the last three decades globally. As with all research, this study had a number of limitations, including the fact that some variations in incidence and mortality may be due to detection biases, such as changes in screening protocols. GBD accounts for ascertainment bias by adjusting single cause estimates to the all-cause mortality envelope. There was data sparsity in some countries such as Iraq and Afghanistan and their estimations were subsequently conducted based on predictive covariates and neighboring locations and should be interpreted with caution. Moreover, HAQ was not available for 2017 and as such we had to examine the association between HAQ and corresponding age-standardised DALY rate for 2016. Finally, there are several other and stronger risk factors for breast cancer, e.g. age at menarche, age at first pregnancy, breast feeding history, use of contraceptives and low number of pregnancies that were not considered in the paper because their associations with breast cancer risk are not fully established.