Women aged 50 to 74 years who get mammograms every other year instead of every year are at a lower risk of false-positive results and at a similar risk of advanced-stage disease.

The study, which was published in JAMA Internal Medicine, identified the outcomes of screening mammography for age, breast density and postmenopausal use of hormone therapy.

Four years ago the U.S. Preventive Services Task Force recommended that breast cancer screening be done every other year as opposed to every one to two years for women aged 50 to 74. However, this guideline only took into account age as a possible risk factor. The American Medical Association says that women should be eligible for screening mammography at the age of 40. It adds that by that age they should have screening covered by insurance.

In this latest study, the researchers, led by Karla Kerlikowske, M.D., of the University of California, San Francisco, aimed to see whether there was any difference in harms or false-positive results among women undergoing mammography in different age groups and with varying breast densities.

  They analyzed a total of 11,474 women with breast cancer and 922,624 women without breast cancer. Data were gathered and examined from various different mammography facilities that belong to the Breast Cancer Surveillance Consortium (BCSC).

The results indicate that biennial mammography wasn't associated with any increase in the risk of advanced-stage tumors compared to annual mammography (regardless of HT use or breast density). Although for women with very dense breasts ages 40 to 49 years, the biennial mammography was linked to a slightly higher risk of advanced-stage cancer.

US Navy 080922-N-2688M-004 Lead Mammography Technologist Carmen Waters assists a patient
Biennial breast screening is associated to fewer false-positive results and a similar risk of advanced-stage disease

The cumulative probability of a false-positive mammography was highest in women with very dense breasts who underwent annual mammography ages 40 to 49 years. It was lowest in women who were 50 to 74 years old with fatty breasts, who underwent either biennial or triennial mammography.

The authors concluded:

".....women aged 50 to 74 years, regardless of breast density or HT use, can undergo biennial rather than annual mammography because biennial screening does not increase the risk of presenting with advanced disease but does substantially reduce the cumulative risk of a false-positive mammography result and biopsy recommendation."

They added:

"Women aged 40 to 49 years with extremely dense breasts who choose to undergo mammography should consider annual screening to decrease the risk of advanced-stage disease but should be informed that annual screening leads to a high cumulative probability of a false-positive mammography result because of the additional screening examinations."

Has breast cancer screening helped reduce death rates?

Studies on whether regular mammographies have contributed to falling death rates have come up with contradictory findings. Breast cancer screening has been and continues to be a controversial subject.

Researchers from the UK, Norway and France believe that breast cancer death rates have dropped because of better treatment and health systems, and not from more mammographies. They wrote in the BMJ (British Medical Journal) (August 2011 issue) that "..breast cancer screening has not played a direct part in the reductions of breast cancer mortality in recent years."

A large-scale Swedish trial found that breast cancer screening does reduce death rates considerably. Stephen W. Duffy, M.Sc., Professor of Cancer Screening, Queen Mary Hospital, University of London, 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."

Written by Joseph Nordqvist