Mammography Has Led to Fewer Late-Stage Breast Cancers, Study Finds
In the past 30 years, since mammography was introduced, late-stage breast cancer incidence has decreased by 37%, a new study published in Cancer has found. The analysis by Helvie et al took into account an observed underlying trend of increased breast cancer incidence present since the 1940s.
Researchers looked at early-stage and late-stage breast cancer diagnoses between 1977 and 1979, the premammography period, and compared it to diagnoses during the mammographic period, from 2007 to 2009. Based on trends observed in the premammography period, as well as continued trends over time, the researchers took into account a central estimated increase in breast cancer incidence of 1.3% per year, the annual percentage change.
In the current paper, the researchers looked at the late 1970s data and projected incidence of early-stage and late-stage breast cancer in 2007 to 2009 based on the annual percentage change. They then compared the projected rates to actual rates.
Decrease in Late-Stage Cancers
Late-stage breast cancer incidence decreased 37% from the projected rate, and early-stage breast cancer incidence correspondingly increased 48% from 1977 through 1979 to 2007 through 2009. They also conducted similar analyses with other annual percentage change values, ranging from 0.5% to 2%. All estimates showed a substantial decrease in late-stage disease.
“When you factor in this temporal trend, our analysis shows that there has been a shift from late-stage to early-stage breast cancer over the last 30 years. This is what you would expect with a successful screening program. Not only are we detecting more early-stage cancer, but we are decreasing the number of late-stage cases that tend to be more challenging to treat and more deadly,” said senior study author Mark Helvie, MD, Professor of Radiology and Director of Breast Imaging at the University of Michigan Comprehensive Cancer Center.
Positive Benefit of Mammography
Prior estimates showed a 1% to 3% annual increase in the United States and Europe before mammography screening began. In countries in Africa, Asia, and Eastern Europe with no routine screening mammography, breast cancer rates are increasing as much as 3% to 5% per year.
Importantly, the current study also found that since mammography was introduced, there has been an overall 9% decrease in invasive breast cancer, when factoring in a 1.3% annual percentage increase. This has been offset by an increase in noninvasive ductal carcinoma in situ.
“While we have seen an increase in overall breast cancer incidence over the last 30 years, the drop in late-stage diagnoses is a positive benefit of mammography and our heightened awareness of early detection. The decrease in late-stage disease, together with improved treatments, contributes to the decreased mortality from breast cancer in the United States in the last 20 years,” Dr. Helvie said.
Dr. Helvie is the corresponding author of the Cancer article.
The study authors reported no potential conflicts of interest.
The content in this post has not been reviewed by the American Society of Clinical Oncology, Inc. (ASCO®) and does not necessarily reflect the ideas and opinions of ASCO®.
