The worldwide use of birth control pills is associated with a decrease in ovarian cancer deaths in the last two decades, especially in the U.S. and Europe, a new study reports. The study predicts that mortality rates will continue to decline because oral contraceptives may offer long-term protection against this type of cancer.

A decline in the use of hormone replacement therapy is also associated with the lower mortality rates, the study said.

The study, “Global trends and predictions in ovarian cancer mortality,” was published by M. Malvezzi and colleagues in the journal Annals of Oncology.

“Over the past two decades, ovarian cancer mortality rates have tended to level off and decrease in several high-income European countries and North America, where rates were highest,” Eva Negri, PhD, ScD, head of epidemiologic methods at the IRCCS Istituto di Ricerche Farmacologiche Mario Negri in Milan, Italy, wrote in the report.

“Advancements in diagnosis and treatment may also have influenced these trends, particularly in high-income countries. However, persisting marked differences in ovarian cancer patterns and trends across various areas of the world remain,” she wrote

Using the WHO database, researchers analyzed death rates by ovarian cancer in patients from 1970 to 2012 (or the most recent year available) in all countries of the European Union except Cyprus, 11 countries from the Americas, including the U.S., and six other countries worldwide. Countries with less than 2 million inhabitants or less than 500 deaths by ovarian cancer from 2005 to 2009 were not included in the study.

In the Americas, the decrease in ovarian cancer deaths was 16 percent (less than 4.9 deaths per 100,000 women in the U.S. and Canada in 2012). Other countries also showed a progressive decline in the number of deaths caused by ovarian cancer (between 2.8 deaths per 100,000 women in Brazil, 4.3 per 100,000 in Uruguay, 3.2 per 100,000 in Japan, 2.3 per 100,000 in Korea, and 4.3 per 100,000 in Australia).

Between 2002 and 2012, European Union countries had approximately a 10 percent decrease in ovarian cancer mortality rates (from 5.8 deaths to 5.2 per 100,000 women).

Sweden was the country with the highest decrease (24 percent) and Poland had the lowest decrease (8 percent). Despite these values, the authors observed that the differences in mortality rates among European countries smaller now than in the 1990s, when there could a threefold difference.

“This is likely to be due to more uniform use of oral contraceptives across the continent, as well as reproductive factors, such as how many children a woman has,” Dr. Carlo La Vecchia, MD, one of the leading authors of the study, said in a news release. “The mixed pattern in Europe also helps to explain the difference in the size of the decrease in ovarian cancer deaths between the European Union and the U.S., as many American women also started to use oral contraceptives earlier.”

In terms of age, the greatest decreases were found in women ages 20 to 49, who showed nearly a 22 percent decline in ovarian cancer deaths in the European Union. Among women ages 50 to 69, the mortality rates declined 11 and 12 percent in Europe and in the U.S., respectively.

In Japan, death rates among younger women also decreased, but not as much as in Europe or the U.S., possibly due to less use of birth control pills. As for women ages 70 to 79, death rates also decreased in the European Union (2.2 percent) and in the U.S. (17.6 percent).

“The use of hormone-replacement therapy declined after the report from the Women’s Health Initiative in 2002 highlighted the increased risk for cardiovascular disease, as well as breast and ovarian cancers, and so this may also help to explain the fall in death rates among middle-aged and older women,” Negri said.

But the good news continue. According to the predictions made by the researchers, by the year 2020, death rates caused by ovarian cancer will be even less frequent, declining 15 percent in the U.S. (to 3.9 deaths per 100,000 women), and 10 percent in the European Union (4.8 per 100,000) and Japan (2.9 per 100,000).

“Other environmental factors, including obesity and diet, have been related to ovarian cancer risk,” the authors wrote. “The quantification of their effect on national mortality rates remains undefined.”