Screening tests: more bad news

Only one in 14 women with a positive mammography result indicating breast cancer will actually have the condition, researchers have discovered. This means that many women are going through needless worry and treatment on the basis of an inaccurate te

The discovery comes at a time when medicine is questioning the value of mammograms and cervical smear testing.

The new attack on mammograms comes from researchers in Canada who analyzed six trials into breast cancer screening. Mammography has been widely welcomed because of the results of two early trials, which claimed a 30 per cent reduction in breast cancer deaths, but four later studies that failed to find any real benefit were ignored.

The real benefits are far more marginal, the Canadian team discovered. Between 7,000 and 63,000 women have to be screened annually to prevent one fewer death from breast cancer. This benefit has to be weighed against the enormous costs and worry associated with the many false readings the test makes (The Lancet, 1995; 346: 29-32).

The US National Cancer Institute stopped recommending mammogram screening in the under 50s in 1993, yet doctors there are still routinely screening women aged between 40 and 49.

A researcher from the University of North Carolina discovered that 89 per cent of doctors in her region were still screening even though they were aware of the change in recommended procedure (The Lancet, June 24, 1995).

This jibes with the results of doctors from Bristol, England, who doubt the benefits of cervical smear screening, a programme they started in 1966 with the aim of eradicating deaths from cervical cancer (see WDDTY vol 6 no 4).

Between 1988 and 1993, nearly 226,000 women were screened, and abnormalities were found in more than 15,000, far higher than the actual rate of cervical cancer which kills one woman in 10,000. Like mammography, cervical screening is causing unnecessary worry to healthy women. "The effect of screening on death rates in Bristol is too small to detect," they conclude (The Lancet, June 10, 1995).