Breast cancer death rates increased by 0.4 percent per year from 1975 to 1989, according to the study. After that, mortality rates decreased rapidly, for a 39 percent drop overall through 2015. The report, the latest to document a long-term reduction in breast-cancer mortality, attributed the declines to both improvements in treatments and to early detection by mammography.

Between 2006 and 2015, the study found that death rates decreased for all racial and ethnic groups tracked — non-Hispanic whites, non-Hispanic blacks, Asian/Pacific Islanders, Hispanics and American Indians/Alaska Natives. But there were substantial variations in mortality between the different groups.

Study co-author R. Edward Hendrick says, “We know that screening mammography saves lives, what’s still a mystery is how many breast cancer deaths are averted by screening mammography and appropriate treatment.”

The researchers estimated how many lives would be saved if every U.S. woman born in 1960 followed one of the three above recommendations each year.

Deaths from breast cancer would fall by an average of 40 percent with annual screenings from 40 to 84, the investigators reported.

By comparison, breast cancer mortality would decline 31 percent with screening until age 79. And it would drop 23 percent with every-other-year mammography from 50 to 74, which is recommended by the U.S. Preventive Services Task Force.

The number of lives saved from breast cancer would be about 29,400 with annual screening from age 40 to 84; and about 22,800 and 17,200, respectively, for the other two recommendations, the researchers found.

Currently, only about half of women over 40 get mammogram screening at least once every two years, even though one in eight is expected to develop breast cancer in their lives, Hendrick said.

Of course, false positive results that require additional and unnecessary screening remain a concern. But, according to Hendrick, “the average woman in her 40s getting annual screening can expect this to occur about once every 12 years.”

As usual, there is still controversy from these findings. Chec with your health professional to determine your next steps, according to your individual family health history. Your guidelines may even be earlier than 40.

*Men at higher risk should get checed beginning at age 35. Men with normal risk, age 40.