U.S. Breast Cancer Screening Data Lead to Questions About the Value of Mammography

Despite some trials showing lower breast cancer–related mortality associated with screening mammography, controversy about its benefit persists, because most trials were conducted decades ago, and screening practices and treatments have changed. Researchers used data on 16 million women (age, ≥40) from 547 U.S. counties to identify the percentage who had undergone mammography in 1999 or 2000 (range, 39%–78% across counties). In these same counties, about 53,000 women were diagnosed with breast cancer in 2000 and were followed for at least 10 years.

Significant correlation was noted between the proportion of county residents screened by mammography and the rate of breast cancer diagnoses, with a 10–percentage-point increase in screening assoc…