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Mammography Screening Reduces Breast Cancer Mortality

June 28, 2011

Breast cancer screening with mammograms has shown proven results in a significant reduction in the number of breast cancer deaths, according to a long-term Swedish study.

The long-running and largest-ever breast cancer screening study has shown that regular mammograms has increased the number of lives saved over time, the research team said on Tuesday.

The study, published online in the journal Radiology, followed more than 130,000 women in two communities in Sweden. An international team of researchers involved in the study found that 30 percent fewer women in the screening group died of breast cancer and the effect persisted year after year.

Now, 29 years after the study began, they found that the number of women saved from the cancer goes up with each year of screening.

“We’ve found that the longer we look, the more lives are saved,” Professor Stephen Duffy of Queen Mary, University of London, told Reuters in a statement.

“Mammographic screening confers a substantial relative and absolute reduction in breast cancer mortality risk in the long-term,” Duffy said in a statement. “For every 1,000 to 1,500 mammograms, one breast cancer death is prevented.”

The Swedish Two-County Trial was the first breast cancer screening trial to show a reduction in breast cancer mortality from screening and mammography alone. The trial randomly separated 133,065 women into two groups, one that received screening and another that received usual care. The screening phase of the trial lasted about 7 years. Women between the ages of 40 and 49 were screened, on average, every 2 years. Woman ages 50 to 74 were screened, on average, every 33 months.

Researchers, nearly 30 years after the trial began, analyzed the original data and the follow-up data to estimate the long-term effect of mammography screening on breast cancer mortality. At 29 years, this represents the longest recorded follow-up period for a mammographic screening study.

Mortality analysis at follow-up points showed a reduction in the breast cancer mortality rate in the screening population, similar to the original trial results. But while the relative effect of screening on breast cancer mortality remained stable over the follow-up period, the benefit in terms of lives saved increased with longer follow-up times. At 29 years of follow-up, the estimated number of women needed to undergo screening every 2 or 3 years over a seven-year period to prevent one breast cancer death ranged from 414 to 519.

“Most of the deaths prevented would have occurred more than 10 years after the screening started,” said Duffy. “This indicates that the long-term benefits of screening in terms of deaths prevented are more than double those often quoted for short-term follow-up.”

“Unfortunately, we cannot know for certain know who will and who will not develop breast cancer,” he noted. “But if you undergo a recommended screening regimen, and you are diagnosed with breast cancer at an early stage, chances are very good that it will be successfully treated.”

Dr. Stamatia Destounis, a radiologist at Elizabeth Wende Breast Care in Rochester, New York, who was not involved in the study, told Reuters that radiologists have been quoting results of the Swedish study for years and the new findings show breast cancer screening is “even more of a benefit than we understood.”

Sweeping changes in the US screening guidelines two years ago that scaled back recommendations on breast cancer screening caused confusion among doctors and patients about the benefits of screening. “We’ve had to do a lot of education of the patients and their doctors. This will help for that,” said Destounis.

New breast screening recommendations issued in 2009 by the US Preventive Services Task Force recommended against routine mammograms for women in their 40s and said women in their 50s should get them every other year instead of every year.

Those guidelines contradicted years of messages about the need for routine breast cancer screening starting at age 40, bringing forth protests from breast cancer experts and advocacy groups who argued the recommendation for fewer screenings would confuse women and result in more deaths from breast cancer.

The latest results from the Swedish study show the rate of false positive results was low.

“We saw the actual number of over-diagnosed cases was really very small — less than 5 percent of the total,” Robert Smith, director of cancer screening at the American Cancer Society and one of the study’s authors, told Reuters in a telephone interview.

The American Cancer Society, among others, have stuck by their long-standing guidelines of yearly breast exams for women in their 40s, stressing that the breast X-rays have been proven to save lives by spotting tumors early, when they are most easily treated.

“I think for anybody who was beginning to have their faith shaken in the value of mammography, these data show mammography is quite valuable as a public health approach to reducing deaths from breast cancer,” said Smith.

Screening women 40 to 54 every 18 months and screening women 55 and older every two years would be a reasonable plan, Duffy said.

The new findings may not speak to the frequency of screening issue, but they do make clear that screening works. “Everyone must make up their own mind, but certainly from combined results from all the screening trials, mammography in women aged 40-49 does reduce deaths from breast cancer,” he said.

Breast cancer is the second-leading cause of cancer death in US women, after lung cancer. Worldwide, more than half a million people die each year from breast cancer and 1.3 million are diagnosed.

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