Å®ÉúСÊÓƵ

Healthy women in the US and Canada are soon to begin a trial of the
drug tamoxifen to see whether it prevents breast cancer. The study, which
will involve 16 000 women, could be under way before a similar trial in
Britain, which has become entangled in a controversy over the drug’s safety.

Samuel Broder, director of the National Cancer Institute in the US,
said the trial was important because it might demonstrate a ‘practical method’
of preventing breast cancer in women at high risk. Half the women in the
trial will take tamoxifen daily for five years; the other half will take
a placebo.

Tamoxifen is effective in treating breast cancer and in reducing the
risk of a woman developing a second tumour in her opposite breast. However,
it also increases the risk of cancer of the lining of the womb and may slightly
increase the risk of blood clots. ‘It is important to stress that tamoxifen,
like any drug, is not without risks in its own right,’ said Broder. ‘Only
a well-controlled clinical trial can answer these important questions.’

Researchers at the NCI expect the incidence of breast cancer will be
reduced by about one-third in the 8000 women receiving the drug. This amounts
to 62 cases of cancer prevented. At the same time, the drug is expected
to cause 38 cases of cancer of the lining of the womb, none of which should
prove fatal, and 3 deaths from thrombosis.

Over the next 10 years, there will be about 1.5 million new cases of
breast cancer in the US and almost half a million deaths. Health officials
agree that preventing the disease is a priority, but for some, the drug’s
risks outweigh its benefits. ‘We oppose the trial as it now stands,’ says
Cindy Pearson of the National Women’s Health Network in Washington DC. ‘It
includes too many women at low risk of breast cancer.’

In Britain, controversy has surrounded the effects of the drug on the
liver. In rats, tamoxifen causes liver tumours and appears to alter DNA
in liver cells (This Week, 29 February and 14 March). However, there have
been only two reported cases of liver cancer in women on the drug. Concerns
over these doubts led the Medical Research Council to withdraw its backing
from the British trial.

But Bernard Fisher, head of the group organising the US trial, repeated
the view expressed by British researchers that the drug is processed differently
in rats than in people. Joachim Liehr, a chemist at the University of Texas
who has studied tamoxifen in rats, disagrees. ‘With repeated doses (of the
drug) three times a day, we found a five- to seven-fold increase in DNA
damage,’ he says. While alterations in DNA are not proven to cause cancer,
he says, ‘additional data from animals would not have hurt before this decision
was made’