快猫短视频

DELAYING the age at which breast cancer screening starts from 45 to 50 might
reduce the risk of X-rays triggering a tumour, say Spanish researchers.

Every year millions of women are screened with X-rays to pick up signs of
breast cancer. If this happens early enough, the disease can often be treated
successfully. According to a survey published last year, 21 countries have
screening programmes. Nine of them, including Australia, Canada, the US and
Spain, screen women under 50.

But the medical benefits of screening these younger women are controversial,
partly because the radiation brings a small risk of inducing cancer. Also,
younger women must be given higher doses of X-rays because their breast tissue
is denser.

Researchers at the Polytechnic University of Valencia analysed the effect of
screening more than 160,000 women at 11 local clinics. After estimating the
women鈥檚 cumulative dose of radiation, they used two models to calculate the
number of extra cancers this would cause.

The mathematical model recommended by Britain鈥檚 National Radiological
Protection Board (NRPB) predicted that the screening programme would cause 36
cancers per 100,000 women, 18 of them fatal. The model preferred by the UN
Scientific Committee on the Effects of Atomic Radiation led to a lower figure of
20 cancers.

The researchers argue that the level of radiation-induced cancers is 鈥渘ot
very significant鈥� compared to the far larger number of cancers that are
discovered and treated. The Valencia programme, they say, detects between 300
and 450 cases of breast cancer in every 100,000 women screened.

But they point out that the risk of women contracting cancer from radiation
could be reduced by between 40 and 80 per cent if screening began at 50 instead
of 45, because they would be exposed to less radiation. The results of their
study, they suggest, could help 鈥渙ptimise the techniques鈥� for breast cancer
screening.

鈥淭here is a trade-off between the diagnostic benefits of breast screening and
its risks,鈥� admits Michael Clark of the NRPB. But he warns that the study should
be interpreted with caution. 鈥淥n the basis of the current data, for every 10
cancers successfully detected and prevented there is a risk of causing one later
in life. That鈥檚 why radiation exposure should be minimised in any screening
辫谤辞驳谤补尘尘别.鈥�

Britain鈥檚 National Health Service screening programme begins at 50. In
1998-99, the latest period for which figures are available, the programme
detected 624 cancers per 100,000 women. According to an NHS spokeswoman, a
British study carried out in 1990 put the number of cancers caused by screening
at 1 in 100,000.

She adds that the radiation a woman absorbs from screening is about the same
as the dose a person receives by flying from London to Australia. 鈥淭he risk that
such a low dose could cause a cancer is negligible and is far outweighed by the
benefits of early detection of breast cancer,鈥� she says.