Most breast cancer deaths seen in non-screened women

NEW YORK (Reuters Health) - Routine mammograms are essential to prevent deaths from breast cancer, as nearly three-quarters of deaths occur in women who don't receive regular screening, according to findings from a large, population-based study.

The study findings were presented Tuesday at a press briefing for the 2009 Breast Cancer Symposium, which is being held later this week in San Francisco.

Randomized trials have suggested that mammographic screening can significantly reduce breast cancer mortality, but the impact of screening on deaths from breast cancer in large general populations was unclear, lead author Dr. Blake Cady, from Cambridge Hospital Breast Center, Massachusetts, told attendees.

The new study featured 6997 women who were diagnosed with invasive breast cancers in Massachusetts from 1990 to 1999. The women were followed through 2007 and breast cancer deaths were determined by review of hospital and outpatient records. Mammography rates in Massachusetts in 1995 were obtained through the Behavioral Risk Factor Surveillance System.

Regular screening was defined as at least two screening mammograms performed at intervals of 2 years or less in asymptomatic women.

During a median follow-up period of 12.5 years, 461 breast cancer deaths were confirmed. Of these deaths, 74.8% occurred in women who did not undergo regular mammographic screening and 25.2% occurred in regularly screened women.

In 1995, roughly 80% of women in Massachusetts over 40 years had undergone mammography in the prior 2 years. Thus, the researchers point out, 75% of breast cancer deaths occurred in the 20% of women who were not regularly screened.

Assuming a 13-year mortality rate of 15% for the 192,740 women diagnosed with breast cancer in 2009, the researchers calculate that the breast cancer mortality rate for regularly screened women will be 5%, while that of unscreened women will be 56%, which is on par with the rate seen in the years before mammography was introduced.

"The most effective method for women to avoid death from breast cancer is to have regular mammographic screening," Dr. Cady concluded.

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