Breast screen benefits need to be revisited

MEDICAL MATTERS:Public anxiety may have been overstimulated

JUST IMAGINE for a moment that the uncertainty over screening for prostate cancer in men was replicated for women attending screening for breast cancer. Would we discourage women attending for mammograms and dismantle the BreastCheck network? The question may not be as fanciful as you think.

The past few years have seen the publication of a number of studies, which, taken together, mean it is time to look again at the benefits of screening women to detect breast cancer.

Most recently, the New England Journal of Medicine published a Norwegian study which found that, while death rates from breast cancer have dropped substantially in recent decades, screening accounts

for just one-third of the reduction.

Researchers looked at four groups of women in Norway, aged 50-69. One group participated in a universal breast-screening programme that was rolled out in stages from 1996 to 2005. Those women were compared with a similar group living in the same area 10 years earlier, before Norway adopted universal screening for breast cancer.

They also looked at a group of women aged 50-69 between 1996 and 2005 but who were living in an area that didn’t yet have the screening programme up and running. Researchers compared that group to another group living in the area 10 years earlier.

Dr Mette Kalager and her colleagues found that breast cancer death rates declined by 18 per cent among the group who did not have access to a universal screening programme, compared with the group from the previous decade. Kalager, a breast surgeon at Oslo University Hospital, noted that the mortality reduction from screening in the study was lower than expected.

In 2008, another study used the introduction of screening in Norway to assess the role of mammography. Researchers compared breast cancer rates among nearly 120,000 women who had three rounds of mammography between 1996 and 2001 with those among nearly 110,000 women in the same age range (50-64) in the five-year period preceding the start of the screening programme.

The two groups of women were carefully matched and so the rates of cancer should have been almost identical. In fact, the women who hadn’t been regularly screened had 22 per cent fewer breast cancers.

Could hormone replacement therapy (HRT) be muddying the waters? Certainly the drop in breast cancer incidence among post-menopausal women mirrors the sudden drop in HRT usage following publication of the Women’s Health Initiative study which showed a link between HRT use, breast cancer and cardiac disease. Canadian research published last month in the Journal of the National Cancer Institute shows that, between 2002 and 2004, breast cancer incidence fell 10 per cent among women aged 50 to 64. In that same time period, sales of HRT fell by half.

Some experts reckon the major improvements in outcome are largely due to better treatment. Greater awareness of the disease may also be playing a part. But we also know from post-mortem studies that many women die of other causes without knowing they had breast cancer. This is also the case for prostate cancer in men, which has led to resistance to the introduction of screening for this cancer. And what if breast cancer treatment has improved to the point where screening no longer has a major impact on mortality?

There is some evidence to suggest we may have already reached that point. Take 1,000 50-year-old women and follow them for 10 years, focusing on real numbers rather than percentages. Without breast cancer screening 995.6 women won’t die from breast cancer. With it, 996 women won’t die, a difference of 0.4 per 1,000.

Interesting to hear the new director of the Cancer Control Programme, Dr Susan O’Reilly, say that breast cancer centres here are now attracting healthy women who do not need screening. Have we overstimulated public anxiety about the disease? Perhaps we should tell women who are not keen to undergo breast screening that, actually, that’s okay.