The plain fact is that most DCIS does not become cancerous - a finding made by pathologists doing autopsies on women who had died of something else. Post mortems show that many women may have DCIS harmlessly in their breasts for years; it is only when DCIS spreads out beyond the duct (it is no longer ‘in situ’) that cancer might begin.

The problem is that doctors don’t know what types of DCIS break out and become carcinogenic, or even how often DCIS turns into cancer.

If left untreated, some DCIS will break out and cancer will develop. But these cases are by far the minority. Most DCIS causes no problems at all.

Nevertheless, doctors almost universally recommend treatment, arguing that it is always ‘better to be safe than sorry’.

Cancer statistician Dr Donald Berry, head of biostatistics at the M.D. Anderson Cancer Center in Houston, Texas, labels this ‘knee-jerk’ medicine.

In the hard-hitting article ‘Epidemiology versus scare-mongering’, UK cancer expert Professor Michael Baum attacked health professionals for scaring women into unnecessary treatment. Baum has 30 years of experience as a breast-cancer surgeon at the Royal Free Hospital and, in his view, if left untreated, as many as 80 per cent of all DCIS cases will never become cancerous (Breast J, 2000; 6: 331-4).

This is backed up by American research aimed at quantifying the true risks of DCIS. Cancer statistician Dr Virginia Ernster, at the University of California at San Francisco, looked back over the death statistics of about 7000 women who had been diagnosed with DCIS, both before and after screening had become widespread. She found that, before the advent of screening, only 3.4 per cent of the women died of breast cancer, with the figure dropping to 1.8 per cent after its introduction. In either case, the 'risk of death was low', commented Dr Ernster (Arch Intern Med, 2000; 160: 953-8).

Cut, poison and burn The usual treatment for DCIS is a combination of the three standard anticancer weapons - surgery, chemotherapy and radiation, often disparagingly dubbed ‘cut, poison and burn’ by their detractors.

Although DCIS is not breast cancer, its treatment regime is similar to what is given for the full-blown disease. Doctors will either recommend surgery to remove the so-called diseased part (lumpectomy) or even to remove the whole breast (mastectomy), followed by chemotherapy and/or radiation (Am J Nurs, 2001; 101: 11).

Nevertheless, a recent review of the evidence by cancer expert Maryann Napoli came to a stark and dramatic conclusion: there is no benefit whatsoever from any conventional treatment for DCIS.

Napoli, who runs the Center for Medical Consumers in New York, surveyed the US mortality rates in women diagnosed with DCIS, and found that just 1 per cent of them died from breast cancer - whether their DCIS was treated or not (Am J Nurs, 2001; 101: 11).

'Seventy per cent of women with a DCIS diagnosis are being overtreated and getting all the downsides of treatment - surgical scars, side-effects of surgery, radiation and tamoxifen,' says Professor Susan Love, cancer expert at the University of California at Los Angeles.

Drug treatment For the past 20 years, the ‘wonder drug’ tamoxifen has been the treatment of first choice for breast cancer. Its mode of action is to attack oestrogen, the hormone that is believed to cause breast cancer. In advanced cases of breast cancer, the drug does appear to have an effect, improving some women’s long-term survival by up to 25 per cent. Results like this have hit the headlines.