Mammography screening effective when data are analyzed correctly

NEW YORK (Reuters Health) – Adding to the current debate about the value of mammography screening for breast cancer, a new report in the February 2nd issue of The Lancet questions the methods used in evaluating the data from the mammography screening trials.

In a previous meta-analysis of breast cancer screening trials, Danish investigators Olsen and Gotzsche concluded that "screening for breast cancer with mammography is unjustified." (see Reuters Health report January 7, 2000)

This analysis has become the focus of the Physicians Data Query, a panel sponsored by the National Cancer Institute, which is considering incorporating the findings by Olsen and Gotzsche into their recommendations. (see Reuters Health report January 24, 2002)

"There are fundamental flaws in the way these researchers analyzed the mammography screening trials," Dr. Claudia I. Henschke from New York Presbyterian Hospital-Weill Cornell Medical Center, told Reuters Health. "Researchers think that screening has an immediate effect, but it doesn't." The deaths that screening prevents are those that would have occurred far into the future, she said.

"By focusing on the cumulative mortality rate, researchers are missing where the effect of screening really lies," Dr. Henschke continued. One needs to look at whether the risk of dying from breast cancer, if it develops, is reduced (case-fatality rate). "When you look at case-fatality rate, you need to look at it long enough to see the effect. That is why cohorts need to be followed for at least 7 years," Dr. Henschke said.

She maintains that many of the studies are too short to see the true case-fatality effect. When Dr. Henschke's team analyzed the data from Swedish study, they saw a positive effect of mammography screening. For women 55 years of age or older, the reduction in breast cancer mortality was 55%; and for women between 45 and 54 years of age, there was a 30% reduction in breast cancer mortality.

"Mammography screening is effective but you have to keep screening," Dr. Henschke said. "The problem is that the right analysis has not been done, the focus has been on the wrong measure and in not understanding where the real effect is found."

Dr. Henschke added that "this is something that we have been trying to address in lung cancer screening, without much success. I hope that these findings on mammography will open the discussion about how screening should be evaluated for any cancer."

Lancet 2002;359:404-406.

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