A mammogram every other year reduces the risk that most women will be incorrectly told they may have breast cancer, without increasing the odds they will be diagnosed with advanced disease, researchers said.
While earlier studies also found biennial mammograms may be as effective as yearly screening, today’s research analyzed a broader group of patients, including those with dense breasts or who had used hormone replacement therapy that can increase cancer risk. Data from almost 1 million women who participated in the Breast Cancer Surveillance Consortium from 1994 to 2008 were reviewed in the study released by JAMA Internal Medicine.
The findings bolster guidelines from the U.S. Preventive Services Task Force, which created a controversy in 2009 by recommending biennial mammograms. The American Cancer Society says women should undergo the screening every year for breast cancer, the most common tumor in women, beginning at age 40. Annual exams boost the number of false positives and biopsies without preventing advanced cancer, the researchers said.
“You really decrease you chance of harm if you screen every two years,” said lead researcher Karla Kerlikowske, a primary care physician and professor of medicine at the University of California, San Francisco. “The fear was that if you do it every two years versus every year, you are going to have a really big tumor when you are diagnosed. The reality is these tumors just don’t grow that rapidly.”
The study found an exception for women 40 to 49 years old with extremely dense breasts. Those patients were about twice as likely to be diagnosed with large tumors or advanced cancer if they skipped mammograms. They also had higher rates of false- positive results. Those women should probably get annual mammograms until 50, when they also can revert to getting screened every other year, the researchers said.
“This study is not about whether you should start screening at 40 or 50, but if you are going to be screened, does it matter if you do it every year or every two years,” Kerlikowske said in a telephone interview. “If you’re in that younger group, with dense breasts, it probably does matter.”
More than 230,000 women will be diagnosed with breast cancer in 2013, and almost 40,000 will die from it, according to the American Cancer Society’s annual report. The number of advanced breast cancers in women younger than 40 has tripled in the U.S. during the past three decades.
The results should help doctors determine the most effective approach for an individual woman, taking into account more than just age, Kerlikowske said. Breast density, a radiographic measure comparing the amount of white versus dark on a mammogram, is particularly compelling, she said.
“We have had a lot of discussions about age, and we need to move beyond it,” she said. “We want to know what is putting a person at risk, and if they are at high risk, what we should do differently.”
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