The study, which was carried out by researchers from Harvard and Dartmouth universities, involved a careful evaluation of cancer registry records from 547 U.S. counties. The records were collected through the National Cancer Institute’s Surveillance, Epidemiology, and End Results registry, with researchers focusing on women over age 40 who had a mammogram between 1998 and 2000.
Just over 50,000 of the women who lived in these counties were diagnosed with breast cancer. Their lives were then followed for a 10-year period. Over that time, 15-percent of the women died of breast cancer, while another one in five died of other causes.
The records showed that the extent of mammogram screening in the 547 counties ranged from 39- to 78-percent. Based on those numbers, researchers expected survival rates to be higher in counties where screening was more prevalent.
However, they were surprised to find “no evident correlation between the extent of screening and 10-year breast cancer mortality.”
In the end, researchers found that mammograms helped find cancer but not reduce the risk of death. “The simplest explanation is widespread overdiagnosis, which increases the incidence of small cancers without changing mortality,” the study’s authors noted in their report. “Even where there are 1.8 times as many cancers being diagnosed, mortality is the same.”
Still, those behind the study are not discouraging women from getting mammograms–they just want them to have realistic expectations. “We do not believe that the right rate of screening mammography is zero,” they wrote.
