Passive smoking 'raises breast cancer risk'
Er, no. The study does not say that. This is what it says:
Our data suggest that extensive exposure to passive smoking may increase breast cancer risk. However, since risk of breast cancer was restricted to the most extensive passive smoking category with no clear dose response, the association with passive smoking should be considered suggestive only and needs confirmation from other studies.
The statistical association between passive smoking and breast cancer in this study is actually about as suggestive as a burka. The associations are all over the place and none of them achieve statistical significance. The main finding, based on a fairly substantial 1,515 cases, show that nonsmokers exposed to secondhand smoke have a nonsignificant relative risk of 1.08. Has epidemiology really got to the point where anything other than a relative risk of exactly 1.00 is considered "suggestive"? (Chance alone dictates that RRs of 1.00 are rare, but epidemiologists don't believe in chance when they want to make a name for themselves.)
The fact of the matter is that there has never been any good evidence that active smoking causes breast cancer, which makes an association with passive smoking somewhat unlikely, to say the least. Nothing has been more closely studied in the last sixty years than smoking and disease. Since breast cancer is the most prevalent form of cancer in the world, if there was a real association with smoking, it would have been spotted long before now.
It hasn't been for want of trying. Anti-smoking campaigners have always been very keen to find an association because the high incidence of breast cancer would allow them to create even more stratospheric estimates of how many lives are lost to smoking/passive smoking than already exist. But, as I wrote in Velvet Glove, Iron Fist, they have always failed to do so.
A 1994 paper published in the British Journal of Cancer found no link between breast cancer and ﬁrst or secondhand smoke, nor did a massive assessment of 53 studies that encompassed 55,515 breast cancer patients in the British Journal of Cancer. The Centers for Disease Control, the American Cancer Society, the IARC, the Australian Medical Journal, the British Medical Journal and the US Surgeon General all agreed that there was no link. Geographical and historical spread of cigarette consumption showed no correlation between breast cancer prevalence and smoking, and while lung cancer rates in women began rising in the US from the mid-1960s, breast cancer rates were unaffected by the post-war surge in female smoking.
Velvet Glove, Iron Fist; p. 237
The authors of this new study even acknowledge the lack of evidence for the smoking/breast cancer hypothesis:
...systematic reviews of epidemiological studies published as of 2002 concluded that there was no overall association between active smoking and breast cancer risk, and attributed conflicting results of individual studies in part to the confounding effects of alcohol.
But add that:
However, recent reappraisals of evidence from recent cohort studies have suggested an increased risk of breast cancer that is independent of the effects of alcohol
In other words, decades of research failed to show anything until a few studies were "reappraised" in the era of anything-goes epidemiology in which eager epidemiologists and fevered advocacy groups leap on every finding, no matter how weak. We are now invited to ignore a mountain of evidence built up over decades in favour of single digit relative risks which hover around 1.00, fail to reach significance and fail to display a dose-response relationship. What a state this field of science is in.
If, fifty years ago, you told the scientists who developed the techniques of epidemiology that you thought "passive smoking raises breast cancer risk" because you'd found a statistically insignificant elevated risk of 8% they'd punch you in the face.
That is all.