Breast cancer is now the most commonly diagnosed cancer in the world. The most recent global cancer burden figures estimate that there were 2.26 million incident breast cancer cases in 2020 and the disease is the leading cause of cancer mortality in women worldwide. The incidence is strongly correlated with human development, with a large rise in cases anticipated in regions of the world that are currently undergoing economic transformation. Survival, however, is far less favourable in less developed regions. There are a multitude of factors behind disparities in the global survival rates, including delays in diagnosis and lack of access to effective treatment.
The World Health Organization’s new Global Breast Cancer Initiative was launched this year to address this urgent global health challenge. It aims to improve survival across the world through three pillars: health promotion, timely diagnosis, and comprehensive treatment and supportive care. In this article, we discuss the key challenges of breast cancer care and control in a global context.
Breast cancer represents a significant global health challenge: it is the most commonly diagnosed cancer in the world with an estimated 2.26 million cases recorded in 2020 and is the leading cause of cancer mortality among females. Although historically considered to be a disease of largely developed countries, over half of breast cancer diagnoses and two-thirds of breast cancer related deaths occurred in the less developed regions of the world in 2020.1 This article explores the reasons for the observed variations in the global burden of breast cancer and the challenges of effective care and control.
Breast cancer incidence is highly correlated with human development. The human development index is a composite measure of life expectancy, education and wealth and is a more useful comparator between countries than income alone. Countries with the highest levels of human development have the highest incidences of breast cancer.1 The global age standardised incidence rate in females is estimated to be 48/100,000, varying from under 30/100,000 in sub-Saharan Africa to over 70/100,000 in Western Europe and North America. Although the relative incidence of breast cancer is highest in the most developed regions of the world, much larger populations in less developed regions mean that over half of all breast cancer cases are diagnosed in low- and middle-income countries, creating a significant burden of disease.
The observed global variations in the incidence of breast cancer need to be considered in the context of the known risk factors for the disease. Age is the most important risk factor and the highest age-specific incidence rates are observed in the oldest females. In the UK, over a third of breast cancer occurs in females over the age of 70, and less than one in five females are under the age of 50 at diagnosis. In less developed countries, by contrast, over half of breast cancer occurs in females under the age of 50. A younger population and a decade shorter life expectancy is the main driver of the average younger age at presentation in less developed countries.4 As life expectancy increases alongside economic development in these regions, we can expect to see an increase in breast cancer incidence.
Other risk factors of importance can be classified into reproductive and non-reproductive factors, which are all influenced by economic development. Breast cancer risk increases with younger age at menarche, older age at menopause, having fewer children and less exposure to breast feeding.5,6 Increased levels of human development tend to lower the average age at menarche by improving average nutritional status which is a key determinant of age of onset of menarche. Non-reproductive risk factors of particular interest for breast cancer include obesity,7 with a doubling of breast cancer risk observed in overweight post-menopausal females, and increased alcohol consumption which is estimated to contribute to approximately 4% of all breast cancer cases diagnosed in 2020.8 Approximately 5–10% of breast cancers have an underlying genetic or hereditary cause such as BRCA1 or BRCA2 mutations, but eight out of nine females who are diagnosed with breast cancer do not have an affected female first degree relative.
Studies examining breast cancer incidence in migrant populations in indigenously white countries suggest that the observed lower breast cancer incidence in ethnic minority females is largely explained by variations in the prevalence of known risk factors for the disease rather than any inherent protection against the disease in these groups.10 As countries in less-developed regions of the world undergo socio-economic transition, factors such as increasing life expectancy, changes in female reproductive patterns, rising obesity rates and other lifestyle associated risk factors will contribute significantly to increasing breast cancer incidence rates.
Breast cancer represents a true global health challenge with considerable unmet medical need. An increasing global burden of breast cancer is unavoidable as incidence rates rise in the less developed regions of the world but poor survival does not need to be inevitable. Sustained and equable improvements in outcomes from this treatable disease require concerted and coordinated initiatives in all parts of the world over the years to come. Future research to identify effective interventions with ongoing evaluation to assess the impact of these efforts is vital to reduce the disparities that are currently observed.