Does screening really save lives?

A new government campaign aims to promote an honest approach to the limitations of breast and cervical screening - but as new doubts surface about the impact on death rates, Jeremy Lawrence asks if screening is still being oversold

Hazel Thornton is capable of striking fear into the heart of any doctor. A skittish, frenetically busy 67-year-old, she knows more about breast screening than a colloquy of oncologists. A cancer specialist of international renown once described her as "the best informed patient in the world".

I can vouch for this, having spent half an hour on the phone having my ear bent by her about the iniquities of the Government's latest effort to tell the truth about breast and cervical screening. In her view, despite its efforts to come clean, the Government is being economical with the truth. The benefits of screening, Mrs Thornton believes, are still being oversold.

This is surprising given that it was the efforts of people such as Mrs Thornton that prompted the Government to launch its campaign last week to promote a new "adult" relationship with women over screening. At the same time, figures published this week showing breast cancer has overtaken lung cancer as the most common cancer in Britain, with 39,500 new cases a year, demonstrate the need to protect women from the ravages of the disease.

Speaking at the launch of two new leaflets to be issued to every woman invited for screening to alert them to the risks, Lord Hunt, the Health Minister, said it heralded a new era of "trust and honesty" between patients and the NHS. "The aim is to provide accurate information on what screening can and cannot achieve so women can make an informed choice. Clearly, screening is not perfect."

Julietta Patnick, national co-ordinator of the NHS cancer-screening programme, spelt out what this meant. A decade ago, she said, the aim was to persuade as many women as possible to take part in screening, whereas the aim today was to inform them so they could decide for themselves. "We see this as the beginning of a more open and adult relationship with women than we have had in the past."

So what do women need to know? This is the question that experts at the screening programme have been wrestling with for 18 months. A balance had to be struck between providing enough information about the downside of screening without being so grim-faced that it put women off.

The problem is that not even the specialists have an answer to some of the questions. To take the most glaring example, breast screening revealed a new disease, ductal carcinoma in situ (DCIS), which had not been recognised before screening was introduced in 1988.

DCIS involves micro-calcification of the milk ducts and is a kind of pre-cancer. Last year, 2,000 cases of DCIS were detected at screening, more than one in five of all "cancers" detected, but 13 years after it was first recognised, doctors are still uncertain how to treat it. In some women, the early changes progress rapidly to invasive cancer and need urgent treatment, but in others, the changes are less threatening and need less radical treatment, or no treatment at all. The problem is that doctors do not know which women are at risk.

Dr Joan Austoker of Oxford University, who helped write the new leaflets about the screening programme, said: "Women are furious when told screening has detected something that doctors do not know how to treat." But there is worse, for many women with DCIS are treated with mastectomy (removal of the breast), while women with a genuine invasive cancer are mostly offered less radical surgery involving removal of the lump and radiotherapy or chemotherapy. So the paradox is that the less threatening condition, DCIS, gets the more aggressive treatment.

Mrs Thornton was diagnosed with DCIS at breast screening in 1991. She had an excision biopsy to remove the affected tissue but refused further treatment. "I preferred to wait and see. If I went on to get an invasive cancer, that would be the time to get treatment," she said.

Ten years on, she goes annually for a clinical breast examination (by hand) but avoids mammography. She accepts that the X-ray screen may pick up smaller cancers sooner, before they can be felt by hand, but says there is no proof that this extends life. It may mean simply that people live with the knowledge that they have cancer for longer but die when they would have died anyway. As a result of becoming so well-informed, she is now in demand as a speaker and committee member representing patients interests, and is visiting fellow at the department of public health of the University of Leicester.

She is bitterly disappointed by the new leaflets, which she campaigned for, describing them as "banal, paternalistic and patronising". She said: "They don't present a balanced view. They promote the view that there is a benefit to screening when the latest evidence suggests there isn't."

The "latest evidence" is a controversial study published in The Lancet last month, a re-analysis of data from a review of seven trials first published a year ago, suggesting that breast screening has not saved lives and has increased "aggressive" interventions such as mastectomy. The findings have been rebutted by the national screening programme, which cites a different two-counties Swedish study that suggests that screening may eventually cut the death rate from the disease by 40 per cent.

However, there is still a long way to go to reach that target. Between 1990 and 1998, the death rate from breast cancer fell by 21 per cent in the UK, and 30 per cent of that fall is thought to be due to breast screening, equivalent to just over 6 per cent. This figure is a lot less than the 25 per cent target reduction in the death rate by the year 2000 set a decade ago.

Mrs Thornton said: "The latest figures show the target reduction has been badly missed yet they are still citing the Swedish study to claim rates will eventually fall by 40 per cent. It is irresponsible and inconsistent. I don't know what the answer is but there is some awfully funny spin going on."

Breast screening still provokes intense debate, but cervical screening is hardly less controversial. Dr Austoker, who spent months testing and refining the leaflets, said 450,000 women a year were given an "abnormal" result on their cervical smear but less than 1 in 100 had cancer. Those figures do not appear in the leaflet because women consulted during the drafting said they were confusing. But as Dr Austoker observed: "Every woman who receives an abnormal result thinks she has cancer. That is a huge false positive rate."

Most abnormal smears have reverted to normal by the time a repeat smear is done, but by that time, women have experienced months of anxiety, beginning with the heart-stopping moment when they get their result. So the judgement women have to make is to balance the high probability of being worried unnecessarily against the low probability of detecting a pre-cancerous change that can be treated. Many might still opt to be screened on that basis, and the figures suggest that the cervical screening programme is saving 1,300 lives a year. But, as the minister said, screening is not perfect.

Women invited for cervical screening – an uncomfortable, undignified and, for many, painful procedure – expect that if they are given the all clear that means they will not develop cancer. Most do not consider that the test could be wrong – and, crucially, have never been encouraged to do so by doctors for fear of damaging confidence in the programme. This was dramatically highlighted by an audit in Leicester earlier this year that revealed that 14 women had died of cervical cancer after being given the all clear in screening tests. The audit revealed not another NHS scandal, as claimed by some sections of the press, but the limited powers of screening.

Histology, the examination of tissue samples, is not an all-or-nothing test like a pregnancy test. It is a matter of identifying patterns and clusters of cells that may only be obvious with hindsight. That is why the audit was done – to help improve the accuracy of screening. But it came as a shock to women who thought a negative smear test was a guarantee against cancer.

So is screening worthwhile? Most experts believe, although the evidence is far from conclusive, that it probably is. What is more questionable is how much harm the screening programmes are causing to save those lives. Mrs Thornton says she would not presume to advise any woman what to do. Instead she insists they must be given full information so they can make up their own minds. Medicine is not an exact science. All patients seek certainty but, regrettably, it is only probabilities that are on offer. Screening may reduce the risk of dying of cancer, but it can't eliminate it.