False-Positive Mammography Differences a Mystery

Statistical methods, screening intervals, and mammogram types do not explain the substantial differences in cumulative false-positive risk between the US and Europe, according to a study published in Cancer Epidemiology.

Researchers from Denmark and the United States undertook a study to determine why approximately half of US women have one false-positive test for every 10 screens, while European women have significantly lower rates of false-positives. Screening interval, mammogram type, and statistical methods were evaluated.

The researchers included 99,455 screens from women first screened at age 50 to 69 in the US Breast Cancer Surveillance Consortium (BCSC) between 1996 and 2010, and from two population-based mammography screening programs in Denmark between 1991 and 2012 (230,452 screens) and 1993 to 2013 (400,204 screens).

The researchers found that the empirical cumulative risk of at least one false-positive test after eight (annual or biennial) screens was 41.9% among the women in the BCSC, 16.1% in Copenhagen, and 7.4% in Funen. The researchers noted that the variation in screening interval and mammogram type did not explain the differences by country. Using the Hubbard method, the model-based cumulative risks after eight screens was 45.1% in BCSC, 9.6% in Copenhagen, and 8.8% in Funen. Using the Njor method, these risks were estimated to be 43.6%, 10.9%, and 8.0%.

The study concluded that statistical method, screening interval, and mammogram type does not explain the differences in occurrence of cumulative false-positive risk between the United States and Europe.