RSNA: Kopans pegs flaws in screening mammo research

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The U.S. Preventive Services Task Force's guidelines issued in 2009 are based on a flawed methodology and ignore the benefits of screening mammography for women aged 40 to 49, argued Daniel B. Kopans, MD, director of breast imaging at Massachusetts General Hospital in Boston, during a scientific session at the 96th annual meeting of the Radiological Society of North America (RSNA), held in Chicago last month.

In November 2009, the USPSTF ignited a firestorm in the breast imaging community when it issued screening mammography recommendations that suggested the annual screening routine shift to a biannual exam for women between the ages of 50 to 74 and eliminate screening entirely for women younger than age 50 and older than age 74. The suggestion that women between 40 and 49 years of age forego screening mammography drew hefty criticism.

Initially selected as a surrogate for menopause, the age of 50 is an arbitrary threshold with no scientific basis, offered Kopans. In fact, screening mammography trials are not designed to allow subgroup analysis of women aged 40 to 49 years. When researchers artificially divide women into subgroups (and report minimal benefits to screening mammography), studies lose statistical power.

An alternate model employs a longer follow-up time to compensate for the lack of statistical power inherent in subgroup analysis. Studies with longer follow-up actually yield a statistically significant mortality reduction for women aged 40 to 49, continued Kopans.

Kopans added that it takes five to seven years for screening mammography to impact the death rate. The breast cancer death rate remained flat from 1940 to 1990, shared Kopans, but has dropped 30 percent since 1990 when screening mammography was more widely recommended and utilized.

In fact, a Norwegian study published in the New England Journal of Medicine in September failed to take lag time in to account when it attributed a mere one-third of the 10 percent reduction in Norwegian breast cancer deaths to the country's screening mammography program. “They published the study with an average followup of 2.2 years,” stated Kopans.

In contrast, a Swedish study published in Cancer in September reported reductions in the breast cancer death rates of nearly 30 percent in a cohort of women aged 40 to 49 after following participants for an average of 16 years.

Kopans concluded with two points: “Therapy only saves lives if cancer if detected early,” and “Seventy-five to 90 percent of women who develop breast cancer each year are not at elevated risk.”