Epidemiology of Breast Cancer

Demographics, incidence and mortality:
- In 2018:
  - An estimated 2.1 million women were newly diagnosed with breast cancer:
    - Approximately one new case diagnosed every 18 seconds
  - Additionally, 626,679 women with breast cancer died
- The global incidence of breast cancer:
  - Has been rising:
    - With annual increases of 3.1%:
      - Beginning with 641,000 cases in 1980 and increasing to greater than 1.6 million in 2010:
        This trend is likely to continue
  - Indeed, the global cancer burden in women:
    - Is increasing in countries regardless of income level:
      - Owing to population growth and an aging population
  - The female population:
    - Accounts for 49.5% of the global population:
      - They form a larger proportion of the population > 60 years of age
    - Furthermore, the epidemiology of advanced breast cancer is a research priority as, in most countries:
      - The number of patients with advanced disease is unknown
    - Cancer registries mostly track diagnosis and deaths but not relapses
    - One study estimated that, in 2017:
      - ~160,000 patients live with advanced-stage breast cancer in the United States alone5
    - The death rates also vary among subtypes of breast cancer:
      - With HER2-positive disease:
        Associated with a higher death rate:
        Followed by the TNBC, luminal A and luminal B subtypes
- Incidence varies worldwide:
  - With higher incidence in high-income regions (92 per 100,000 in North America) than in lower income regions (27 per 100,000 in middle Africa and eastern Asia):
    - These patterns reflect both:
      - The risk factors and the availability and utility of mammography (and, therefore, detected breast cancers)
    - The highest breast cancer incidence is in:
      - North America
      - Australia
      - New Zealand
      - Northern and western Europe
  - Furthermore, in high-income countries:
    - Breast cancer is often diagnosed at an early stage and the prognosis is usually good
  - However, in low- and middle- income countries:
    - Breast cancer is often diagnosed at a later stage:
      - And is accordingly, associated with poorer survival:
        A fact that is reflected in the mortality statistics
    - Breast cancer mortality is usually higher in many low- and middle-income countries:
      - Such as those in sub-Saharan Africa and developing Asian countries:
        Despite their lower incidence:
        Due to delayed presentation, late stage at diagnosis and limited access to treatment
  - Several studies have also shown that breast cancer presents:
    - Earlier in Asian women (typically 40 to 50 years of age) than in their western counterparts (typically 60 to 70 years of age)
  - In addition, patients in developing countries who are diagnosed with breast cancer:
    - Are roughly 10 years younger than those in developed countries:
      - The proportion of young patients ( less than 35 years of age) varies from:
        ~10% in developed countries to up to 25% in developing Asian countries
  - The biology of the tumor also varies by ethnicity:
    - Which has implications for the difference in mortality:
      - African and African-American women:
        Have the highest rates of TNBC compared with any other ethnic group
        They also had higher rates of metastatic disease
        They have the highest rates of poorly differentiated or undifferentiated grade among all subtypes:
        All of which are associated with lower survival
      - Additionally, metastatic breast cancer represents 9% of diagnoses among non-Hispanic black women:
        Compared with 5% to 6% of diagnoses in other ethnic groups
      - Regarding the survival gains in patients with advanced disease during the years 1975 to 2013:
        The 5-year cause-specific survival of non-Hispanic white women was higher than that of other ethnic groups:
        Particularly non-Hispanic black women (19% to 37% com- pared with 16% to 26%):
        This pattern is multifactorial and involves genetic predisposition, lifestyle and other environmental factors
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