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Excerpts from Smoke screen; A link between passive smoking and breast cancer? One man whose opinion counts thinks the research is right and is willing to risk his reputation to spread the word

By MARK RAGG, Sydney Morning Herald [11/24/99]

Richard Burton's cause is research published earlier this year suggesting that passive smoking by girls around the age of puberty causes breast cancer later in life.

As director of the Anti-Cancer Council of Victoria, Burton's views count, and his speech will put smoking firmly on the breast cancer agenda.

It is certainly not there at the moment. In 1995, two remarkably comprehensive reports on smoking were published. The first quantified drug-caused morbidity and mortality in Australia. Commissioned by the Federal government and carried out by Western Australian public health experts Dr Dallas English and Professor D'Arcy Holman, it looked at the scientific evidence on smoking. The second report, Tobacco in Australia: Facts and Issues, came from anti-smoking activists Margaret Winstanley and Stephen Woodward.

English and Holman examined the only 14 studies they judged worthwhile, and said there was "inadequate evidence that smoking causes breast cancer". Winstanley and Woodward don't even mention breast cancer in connection with smoking. If there was any evidence by 1995, it would have found its way into those two reports.

The first glimmer came in 1996, when Swiss researchers published a study in the American Journal of Epidemiology showing that both active and passive smokers doubled their risk of breast cancer. Then, early this year, Timothy Lash and Ann Aschengrau from the Boston University School of Public Health published another paper in the same journal which provided strong evidence.

Lash and Ashengrau believed smoke could cause problems for a young girl's breasts, so they asked women with breast cancer about their first exposure to passive smoke. Basically: did your parents smoke in the house? A simple question, but they were the first to ask it. They found that women whose parents smoked at home - usually fathers at that time - were far more likely to have breast cancer than women whose fathers did not smoke.

But the research has appeared with very little fanfare. Why? Perhaps the answer lies in its publication date - New Years Day. Who reads medical journals with a sore head? So the research just disappeared into the ether, exciting some like Burton, but generating no public interest because the public didn't know about it. Burton has run with it now because he believes it important and wants to carry out similar research in Australia. He believes he'll have an answer by the end of next year.

The research appears plausible and has the three things any epidemiological study needs.

The first is a statistical association - that women breathing in smoke, in whatever form, get breast cancer more often that women who breathe little smoke. It has that.

The second is a positive dose-response relationship - the study has to show that women who smoke lots have more cancer than women who smoke only a bit. It does that.

The third is plausibility. For example, epidemiologists could show that mobile phone use is highest in countries with lots of breast cancer. Do mobiles somehow burn breasts? Unlikely. But it's true that breast cancer is associated with wealth and so are mobiles.

The Swiss nominate two chemicals found in cigarette smoke as possible culprits. They say benzo(a)pyrene is a well-known carcinogen. And 7,12-dimethylbenzo(a)anthracene is a chemical used in standard laboratory tests to cause breast cancer in rats. These chemicals could be absorbed by people breathing smoke, enter the bloodstream and become concentrated in breast tissue, irritating cells and eventually causing cancer.

If all this happens early in life, breast cells would start multiplying in puberty and be most susceptible to carcinogens at a time when they are surrounded by them.

Lash and Aschengrau add an interesting twist. Older women who smoke may protect themselves, marginally, against breast cancer because they delay menopause. Delaying menopause delays the surge in breast cancer that comes after menopause.

Burton says this explains why Lash and Aschengrau have managed to show something nobody else had shown - other researchers were posing the wrong question. He says that comparing smokers to non-smokers is the wrong approach if passive smoking causes breast cancer, because the control group still contained plenty of women who were smoking, albeit passively.

An analysis of all six studies on passive smoking and breast cancer since 1985, due to be published soon in the journal Cancer Causes and Control, provides "pretty convincing evidence", he says.

The fascinating part of this research, if supported, is the knock-on effect. Associate professor Simon Chapman, chairman of lobby group Action on Smoking and Health, says a link between breast cancer and smoking would have a huge impact.

Tobacco companies have recently switched their defence against both litigation and social controls from "cancer, what cancer?" to "you're all big kids - you knew the risks".

If passive smoking causes breast cancer, that defence just won't hold.