Mammogram Benefit Greater than Originally Thought

New data released by the American Cancer Society indicates that women who have mammograms regularly can reduce their risk of dying from breast cancer by more than 60%, suggesting that mammograms "do substantially more good than most experts had assumed up to now," the AP/Owensboro Messenger-Inquirer reports. Previous "landmark" studies performed in North America and Europe during the 1970s and 1980s have shown that mammograms reduce risk of breast cancer mortality by about 30%. But in those studies, the difference between women who had mammograms and those who did not was "diluted" because some women who were offered screenings refused to get them and others in unscreened comparison groups got mammograms on their own. The latest analysis, based on 6,807 Swedish women ages 20-69 who were diagnosed with breast cancer over a 30-year study period, examined what happened to women who did get mammograms.

Researchers compared mortality rates in three time periods, 1968-1977 (before mammograms' introduction), 1978-1987 (mammograms offered to half the women in the study) and 1988-1996 (mammograms available for all women over age 40 every two years). Researchers determined that women who comply with screening recommendations reduce their risk of dying from breast cancer by 63%, compared to the early 1970s, when mammograms were not routine. During the last study period, 85% of women got regular mammograms. Epidemiologist Robert Smith, director of cancer screening for the American Cancer Society, said, "Women should be told that if they get regular screening, they will reduce their risk of dying from breast cancer by about two-thirds." He added that although some researchers have questioned whether the reduced mortality risk is the result of catching the disease earlier or from better treatments, the study data suggest that "screening accounts for nearly all the benefit." There is no "significant increase in survival" in either breast cancer patients who are too young for mammograms or older women who refuse to get them, he said. Dr. Marilyn Leitch of the Dallas-based University of Texas Southwestern Medical Center, added, "The contribution of treatment advances is there. But I think a large part of the improvement is related to the screening benefit."

Other researchers questioned the study population, saying that examining only women who get mammograms "opens the possibility of ... selection bias" because women who get mammograms could already be healthier than women who do not. Thus, it could be their "good habits, not their mammograms, that make them live longer," the AP/Messenger-Inquirer reports. But Smith said selection bias "is unlikely to have made a big impact on the [mortality] reduction seen in the study" (Haney, AP/Owensboro Messenger-Inquirer, 4/24). Smith said that care providers should step up efforts to increase mammography rates, concentrating on those women in groups with the highest mortality rates. He added, "It is important to give women advice today based on the best possible evidence we have. What we do have is a proven technology that is not evenly applied" (Crane, Columbus Dispatch, 4/24). The results of the analysis will be published in the May 1 issue of the journal Cancer (AP/Owensboro Messenger-Inquirer, 4/24).