Researchers suggest that contrasts in healthcare systems and patient management between similar countries could explain disparities in breast cancer death rate.
The results of the study were recently presented at the American Association for Cancer Research 2016 San Antonio Breast Cancer Symposium in Texas.
The United Nations agency maintains that the cornerstone of breast cancer control is early detection in order to improve outcomes and survival.
Cécile Pizot - of the International Prevention Research Institute in Lyon, France, and lead author of the new study - says that worldwide, breast cancer accounts for a quarter of all cancers in women.
"Comparing mortality trends between countries helps identify which healthcare systems have been the most efficient at reducing breast cancer mortality," she notes.
Using WHO worldwide data, she and her colleagues calculated rates of breast cancer deaths for 1987-2013 for different age groups.
Biggest decline in deaths occurred in England and Wales
The analysis shows that deaths to breast cancer fell in 39 of 47 countries - including the United States and most of the developed countries in Europe.
- In the U.S., an estimated 246,660 new cases of invasive breast cancer will be diagnosed in women in 2016
- There are currently over 2.8 million breast cancer survivors in the U.S.
- The chance that a woman in the U.S. will die from breast cancer is about 1 in 36.
The biggest decline in breast cancer deaths over the 26-year period - a drop of 46 percent - occurred in England and Wales.
Pizot says this was no surprise, because of the improvements there have been in detection and treatment over recent decades.
The analysis also highlights disparities in other parts of the world. For instance, in Latin America, while breast cancer rates for women of all ages have dropped in Argentina and Chile, they have gone up in Brazil and Colombia.
The steepest increase in breast cancer mortality occurred in South Korea - both overall and in individual age groups. In total, the East Asian nation has seen an 83 percent rise in breast cancer deaths in the 1987-2013 period.
However, the proportion of women who die from breast cancer every year is still lower in South Korea than in the U.S. - 5.3 per 100,000 versus 14 per 100,000, respectively, during 2011-2013.
Pizot comments there has been a major shift in South Korea since the mid-20th century. Once a largely agrarian nation, it has become highly industrialized and westernized. She notes:
"Such quick changes might explain the considerable shift in cancer mortality."
No clear link to screening
Analysis by age shows that global mortality fell more for women under 50 than over 50. Pizot says this could be due to younger women receiving more intensive treatment - such as longer courses of chemotherapy - which can result in longer survival that extends into later years.
Looking more closely at the figures for the U.S., the researchers find that deaths to breast cancer fell by 42 percent. In 1987-1989 there were 22 deaths per 100,000 women, which dropped to 14 per 100,000 in 2011-2013.
Rates of death to breast cancer fell for women in the U.S. across all age groups over the period, halving in women under 50, falling by 44 percent in the 50-69 age group, and falling by 31 percent in those aged 70 and over.
The researchers note that there appears to be no clear link between screening and rates of death to breast cancer.
Pizot says they found several examples of little difference between countries of similar geographic location and wealth, even though one had introduced mammography screening considerably earlier than the other (for instance, the 1980s versus 2005).
She suggests their analysis highlights the difficulties of pointing to a single factor with a strong effect on breast cancer death rates. Future studies should look more closely at particular aspects of disease management - such as risk factors, types of drugs, access to care, and the use of multidisciplinary teams.
"Differences in healthcare systems and patient management could explain discrepancies in mortality reduction between similar countries. However, there is at present little data comparing the management of breast cancer patients across countries."
A limitation of the study is that the analysis left out countries because of lack of data for nations in Latin America, Asia, and Africa.