As researchers and clinicians attempt to discern the impact of mammography screening and relative contributions of screening and treatment to mortality improvements, a Dutch study demonstrates both screening and treatment contribute to reduced mortality. Even with improved treatments for the disease, population-based mammography programs still save a significant number of lives, according to a study evaluating the effectiveness of breast cancer screening presented March 21 at the Eighth European Breast Cancer Conference in Vienna.
Rianne de Gelder, PhD student and researcher at the Erasmus University Medical Center in Rotterdam, The Netherlands, and colleagues used computer modeling to show that adjuvant treatment reduced deaths from breast cancer from 67.4 per 100,000 woman-years to 57.9 in 2008.
The researchers explained in the study abstract that adjuvant therapy reduced deaths by an estimated 13.9 percent in 2008 compared to no treatment; but they also found that screening every two years reduced deaths by an additional 15.7 percent.
With the addition of two annual screening exams between the ages of 50 to 75, the deaths fell to 48.8 per 100,000 woman-years, meaning that adjuvant therapy combined with screening reduced deaths by a total of 27.4 percent.
If screening were to be extended to women between ages 40 and 49, deaths would reduce by a further 5.1 percent, according to de Gelder and colleagues. Thus the total reduction in breast cancer deaths would be 31.1 percent compared to a situation where there was no treatment and no screening for women aged 40 to 75.
"The effectiveness of breast cancer screening has been heavily debated in the last couple of years. One of the arguments that critics have is that, since breast cancer patients can be treated so effectively with adjuvant therapy, the relative effects of screening become smaller and smaller. Our study shows that, even in the presence of adjuvant therapy, mammography screening (between ages 50 and 75) is highly effective in reducing breast cancer deaths—and, in fact, is slightly more effective than adjuvant treatment. Screening women of these ages should definitely continue,” de Gelder said.
"In addition, if screening could be started before the age of 50, the breast cancer mortality could be further reduced, even when breast cancer patients are effectively treated by adjuvant therapy. It has the potential to further decrease breast cancer mortality by up to 5.1 percent when 10 additional annual screening examinations starting from age 40 are performed. Policy makers should investigate further the ideal age for starting screening, taking into account not only the effects, but also the risks and costs of extending the lower age limits."
The microsimulation computer model that the researchers used was created using both Dutch and international statistics on breast cancer incidence; survival and mortality; screening programs, including rates of cancer detected by screening and those that were diagnosed in between screenings; and the use and effectiveness of adjuvant breast cancer treatments. Breast cancer mortality in the model was also based on Dutch mortality data between 1975 and 2008, and so included data from the period in which women were not screened and hardly ever received adjuvant therapy, as well as the period in which women could have been screened and treated with adjuvant therapy.
“It is important to note that our study demonstrated that the observed reduction in breast cancer mortality in The Netherlands could not fully be explained by mammography screening and adjuvant therapy only," concluded de Gelder. "Other, unknown causes are likely to have contributed to fewer deaths as well. These causes may, for instance, include further developments in breast cancer diagnostics and treatment. It may also be possible that the effects of screening and adjuvant treatment are even larger than currently assumed in the model."