Treatment Advances Averted More Than Half a Million Breast Cancer Deaths Over 3 Decades

As many as 614,500 breast cancer deaths have been averted since 1989, according to a new study. This figure can be attributed to greater usage of preventive screening measures as well as advancements in treatment.

Beginning in 1969, the National Cancer Institute’s Surveillance, Epidemiology, and End Results (SEER) program has annually gathered data on the frequency of breast cancer and associated mortality rates in the United States. It was observed that these rates among afflicted women increased 0.4% annually from 1975 to 1990. It was then found that mortality rates began to decrease 1.8% per year from 1990 to 1995, 3.4% from 1995 to 1998, and 1.8% from 1998 to 2015. Cumulatively, breast cancer mortality rates among females between the ages of 40 and 84 dropped by 41.6% from 1989 to 2015.

The authors applied age-adjusted population and mortality rate data from the SEER program to predict the total amount of breast cancer deaths avoided by preventive screening and advancements in treatment from 1989 to the present. Four different assumptions about background mortality rates were applied to approximate deaths avoided for women between 40 and 84 years old. These assumptions included an increase of 0.94% per year in the absence of screening or treatment, an increase based on the trend from 1979 to 1989, an increase of 0.4% per year based on what was observed from 1975 to 1990, and a flat mortality rate since 1989. The approximations were calculated by measuring the difference between SEER-reported and background mortality rates for each 5-year age group then multiplied by the population for each group.

SEER data was used to project total yearly breast cancer deaths deterred in 2012 and 2015 and estimated SEER data was used to evaluate deaths avoided in 2018. Based on the aforementioned assumptions, research conducted by the authors has shown the total number breast cancer deaths prevented since 1989 ranged from 237,234 to 370,402 in 2012, from 305,934 to 483,435 in 2015, and from 384,046 to 614,484 in 2018. Applying the same assumptions to the approximated amount of total lives saved in a singular year, data shows these numbers fall between 20,860 to 33,842 in 2012, 23,703 to 39,415 in 2015, and 27,083 to 45,726 in 2018.

Breast cancer mortality rates steadily increased prior to 1990, according to the data. In the 1980s, advances in treatment, including chemotherapy and hormonal therapy, entered clinical practice. It is estimated that together they were successful in reducing mortality rates by 1989.

During the same time period, physicians began to advocate that early detection was also crucial for saving lives. As a result, screening mammography grew in popularity and had started becoming broadly clinically practiced. While the long-term benefits of mammography became invaluable to thousands of lives, at its introduction, research shows preventive screening, “was shown by randomized controlled trials to require 5 to 7 years to demonstrate an evident mortality reduction due to the longer interval between screen detection and prevented death.” Therefore, significance of the effect of these screenings on the reduction of mortality rates was only measurable after 1990.

The prevalence of mammography screening has drastically fluctuated since its inception. Data released by the CDC’s National Health Interview Survey show that in 1987, 29% of women over 40 years old attended screening within a 2-year window. The same survey reported mammography was at the height of its popularity in the year 2000, at 70%, then alarmingly fell to 64% in 2015. Presently, only about half of women over 40 years old receive recommended screening mammography.

“The best possible long-term effect of our findings would be to help women recognize that early detection and modern, personalized breast cancer treatment saves lives and to encourage more women to get screened annually starting at age 40,” R. Edward Hendrick, PhD, of the University of Colorado School of Medicine, said in a statement.

Reference

Hendrick RE, Baker JA, Helvie MA. Breast cancer deaths averted over three decades [published online February 11, 2019]. Cancer. doi: 10.1002/cncr.31954.