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Spokane, Washington  Est. May 19, 1883

Study: Increased mammograms may not decrease cancer deaths

Karen Kaplan Los Angeles Times

The increased use of mammograms to screen for breast cancer has subjected more women to invasive medical treatments but has not saved lives, a new study says.

After reviewing cancer registry records from 547 counties across the United States, researchers concluded that the screening tests aren’t working as hoped. Instead of preventing deaths by uncovering breast tumors at an early, more curable stage, screening mammograms have mainly found small tumors that would have been harmless if left alone.

“The clearest result of mammography screening is the diagnosis of additional small cancers,” researchers reported Monday in the journal JAMA Internal Medicine. “These findings suggest widespread overdiagnosis.”

The researchers, from Harvard and Dartmouth, examined data from the National Cancer Institute’s Surveillance, Epidemiology, and End Results registry. Counties were included in the study if they reported the percentage of women ages 40 and above who had a screening mammogram between 1998 and 2000.

Among the more than 16 million women who lived in these counties, 53,207 were diagnosed with breast cancer in 2000 and then tracked for the next 10 years. During that time, about 15 percent of them died of breast cancer and 20 percent died of other causes.

The researchers found that the extent of screening in the 547 counties ranged from 39 percent to 78 percent. Ideally, the counties with more widespread screening would have lower rates of breast cancer deaths.

Instead, the researchers found “no evident correlation between the extent of screening and 10-year breast cancer mortality,” they wrote.

For every 10-percentage-point increase in screening rates, the incidence of breast cancer rose by 16 percent, according to the study. That worked out to an extra 35 to 49 breast cancer cases for every 100,000 women.

Most of those tumors were considered small, measuring less than 2 centimeters across. But there was no corresponding decrease in larger tumors, the result that would have been expected if mammograms were catching cancers before they grew to a more threatening size.

The researchers also examined breast cancers according to their stage at diagnosis, a marker of a tumor’s aggressiveness. More screening was associated with a higher incidence of early-stage breast cancers but no change for later-stage tumors, according to the study.

“The simplest explanation is widespread overdiagnosis, which increases the incidence of small cancers without changing mortality,” the study authors wrote. “Even where there are 1.8 times as many cancers being diagnosed, mortality is the same.”

The study did not consider cases where mammograms were used to find breast cancers in women who had symptoms of the disease, such as a suspicious lump.

The study authors maintained that mammograms are a valuable tool to screen women for breast cancer.

“We do not believe that the right rate of screening mammography is zero,” they wrote.