Mammography screening significantly reduces breast cancer death rates


Mammography screening significantly reduces breast cancer death rates

Mammography breast cancer screening reduces death rates significantly in the long-term, researchers report in the journal Radiology. A large-scale Swedish trial found that for the benefits to be appreciated, studies need to evaluate screening over the very long term.

Professor of cancer screening at Queen Mary, University of London, Stephen W. Duffy, M.Sc., said:

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

The authors explained that this - The Swedish Two-County Trial - was the first study to demonstrate a drop in breast cancer mortality from just screening with mammography. It involved 133,065 women who were randomly selected into two groups:

  • Invitation group - they received an invitation to screening
  • Usual care group - they received usual care
The researchers found that there were 30% fewer deaths caused by breast cancer in the invitation group, compared to the usual care group. The 30% lower death rate included the women who did not attend (those who were invited but did not undergo screening). The screening phase of the study lasted about 7 years.

The female participants aged 40 to 49 were screened every two years, while those aged 50 to 74 underwent screening every 33 months (average in both cases).

The authors analyzed data and follow-up data 29 years after the beginning of the trial to work out what the long-term effect of mammography screening on breast cancer mortality might be. They say that theirs is the longest recorded follow-up period ever for mammography screening.

The status of each case, as well as cause of death were determined by local trial end point committees, as well as an independent external committee.

The authors explained:

"Mortality analysis at follow up 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 absolute 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.

The scientists say that follow-up times need to be very long term, at least 15 to 20 years. Only then can real reductions in mortality rates be observed.

Duffy said:

"Most of the deaths prevented would have occurred more than 10 years after the screening started. 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."

Doctors should use these new data when explaining the long-term benefits of breast cancer screening to their adult female patients, the authors added.

Duffy said:

"Unfortunately, we cannot know for certain who will and who will not develop breast cancer. 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."

"Swedish two-county trial: Impact of mammographic screening on breast cancer mortality during three decades"

Stephen W. Duffy, M.Sc, László Tabár, M.D., Bedrich Vitak, M.D., Tony Hsiu-Hsi Chen, Ph.D., Amy Ming-Fang Yen, Ph.D., Anders Cohen, M.D., Tibor Tot, M.D., Sherry Yueh-Hsia Chiu, Ph.D., Sam Li-Sheng Chen, Ph.D., Jean Ching-Yuan Fann, Ph.D., Johan Rosell, Ph.D., Helena Fohlin, M.Sc., and Robert A. Smith, Ph.D.

Radiology. 2011;doi:10.1148/radiol.11110469.

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Section Issues On Medicine: Women health