1.1.1 Incidence and Death of Breast Cancer Worldwi...
Cancer is a leading cause of death in both more and less economically developed countries；the burden is expected to grow worldwide due to the growth and aging of the population，particularly in less developed countries，in which about 82%of the world's population resides.Based on GLOBOCAN estimates，about 14.1 million new cancer cases and 8.2 million deaths occurred in 2012 worldwide.Lung and breast cancer are the most frequently diagnosed cancers and the leading causes of cancer death in men and women.［1］In 2018，there is an estimated 18.079 million new cancer cases and 9.555 million cancer deaths.Compared with 2012，the incidence and mortality of malignant tumors were both on the rise.［2］It is estimated that nearly one-half of the cases and over one-half of the cancer deaths in the world will occur in Asia in the year 2018，in part because close to 60%of the global population resides there［2］.Europe accounts for 23.4%of the total cancer cases and 20.3%of the cancer deaths，although it represents only 9%of the global population，followed by the Americas'21%of incidence and 14.4%of mortality worldwide.In contrast to other regions，the shares of cancer deaths in Asia（57.3%）and Africa（7.3%）are higher than the shares of incidence（48.4%and 5.8%，respectively）because of the different distribution of cancer types and higher case fatality rates in these regions.In 2018，lung cancer is the most commonly diagnosed cancer（11.6%of the total cases）and the leading cause of cancer death（18.4%of the total cancer deaths），closely followed by female breast cancer（11.6%），colorectal cancer（10.2%），and prostate cancer（7.1%）for incidence and colorectal cancer（9.2%），stomach cancer（8.2%），and liver cancer（8.2%）for mortality.
Breast cancer is the most frequently diagnosed cancer and the leading cause of cancer death among females worldwide.Over the past 20 years，breast cancer rates have increased in most countries.［3］Based on GLOBOCAN estimates，about 1.677 million cases and 522，000 deaths are in 2012［1］.By 2018，there will be an estimated 2.089 million new cases，accounting for 25%of all cancer cases，and 627,000 deaths，accounting for 15%of all cancer deaths among females.［2］The disease is the most frequently diagnosed cancer in the vast majority of the countries（154 of 185）and is also the leading cause of cancer death in over 100 countries（Figs.5B and 6B）；the main exceptions are Australia/New Zealand，Northern Europe，Northern America（where it is preceded by lung cancer），and many countries in Sub-Saharan Africa（because of elevated cervical cancer rates）.Breast cancer incidence rates are highest in Australia/New Zealand，Northern Europe（eg，the United Kingdom，Sweden，Finland，and Denmark），Western Europe（Belgium［with the highest global rates］，the Netherlands，and France），Southern Europe（Italy），and Northern America（Fig.9）.In terms of mortality，breast cancer rates show less variability，with the highest mortality estimated in Melanesia，where Fiji has the highest mortality rates worldwide.［2］(https://www.daowen.com)
Although hereditary and genetic factors，including a personal or family history of breast or ovarian cancer and inherited mutations（in BRCA1，BRCA2，and other breast cancer susceptibility genes），［4-5］account for 5%to 10%of breast cancer cases，studies of migrants have shown that nonhereditary factors are the major drivers of the observed international and interethnic differences in incidence.Comparisons of low-risk populations migrating to high-risk populations have revealed that breast cancer incidence rates rise in successive generations.［6］Elevated incidence rates in higher Human Development Index（HDI）countries are attributed to a higher prevalence of known risk factors and the elevated incidence rates in transitioned countries are the consequence of a higher prevalence of known risk factors related to menstruation（early age at menarche，later age at menopause），reproduction（nulliparity，late age at first birth，and fewer children），exogenous hormone intake（oral contraceptive use and hormone replacement therapy），nutrition（alcohol intake），and anthropometry（greater weight，weight gain during adulthood，and body fat distribution）；whereas breastfeeding and physical activity are known protective factors.［7-8］
Incidence rates of breast cancer have been rising for most countries in transition over the last decades，with some of the most rapid increases occurring where rates have been historically relatively low，in transitioning countries in South America，Africa，and Asia［9］.These trends likely reflect a combination of demographic factors allied to social and economic development，including the postponement of childbearing and having fewer children，greater levels of obesity and physical inactivity，and increases in breast cancer screening and awareness.In several developed countries，including the United States，Canada，the United Kingdom，France，and Australia，the fall in incidence in the early 2000s was partly attributable to declines in the use of postmenopausal hormonal treatment after publication of the Women's Health Initiative trial linking postmenopausal hormone use to increased breast cancer risk，as first reported in the United States.［10-11］The primary risk factors for breast cancer are not easily modifiable because they stem from prolonged，endogenous hormonal exposures，although prevention through the promotion of breastfeeding，particularly with longer duration，may be beneficial.