A study published in Cancer found that since health care providers began using mammography more than 30 years ago, the number of people diagnosed with advanced-stage breast cancer has decreased by 37 percent.
Using data from the National Institutes of Health SEER database, researchers from the University of Michigan looked at early-stage and late-stage breast cancer diagnoses between 1977 and 1979, before mammography became a standard screening tool, and then again for diagnoses between 2007 and 2009.
The study's authors also took into account that since 1977, breast cancer diagnoses have increased about 1.3 percent per year. Using this annual percentage change and the data from the 1970s, they estimated how many early- and late-stage diagnoses there would be 30 years later. They then compared the results to the actual number of diagnoses between 2007 and 2009.
The study found that the actual number of advanced-stage breast cancer diagnoses decreased by 37 percent from 1977 to 2009, while the number of early-stage diagnoses increased 48 percent. The study also found that since mammography became the standard of care, there has been a 9 percent decrease in invasive breast cancer.
Researchers said the results suggest that mammograms are finding more breast cancers in their early stages, when they are typically easier to treat and less likely to be terminal. The authors said the drop in late-stage diagnoses proves the benefits of annual mammography screening.