Research News Alert
John Wiley & Sons, Inc.
June 2, 2005
For Immediate Release[...]

Contact: David Greenberg

Long-term exposure to passive smoking may increase premenopausal breast
cancer risk

Breast cancer is one of the most commonly diagnosed cancers among women in
Western countries. In North America, for example, there are an estimated
233,000 new cases every year and 45,000 deaths. Despite the
well-characterized role of genetics and reproductive risk factors, as well
as the suggested roles of physical activity and alcohol, more than half of
breast cancer risk remains unexplained. A new study, published online May
31, 2005 in the International Journal of Cancer, the official journal of the
International Union Against Cancer (UICC), suggests that long-term exposure
to passive smoking (second-hand smoke) may increase premenopausal breast
cancer risk. The study is available via Wiley InterScience at[...] .

Researcher Kenneth C. Johnson, Ph.D. of the Public Health Agency of Canada,
which is part of the Government of Canada, analyzed data from the 20
published studies which had examined the relationship of passive smoking to
breast cancer. Most but not all of the 20 studies reported increased risk,
leading the author to explore what might explain the differences in observed
risks among the studies. Factors he evaluated included the impact of study
design (case-control or cohort); when the study was published (before or
after the year 2000); where the study was conducted (Asia, Europe, North
America); what outcome measure was used (breast cancer death or diagnosis);
and the quality of the second-hand smoke exposure measure.

The completeness of the second-hand smoke measures varied widely. Studies
that collected quantitative long-term information on the three major
potential lifetime sources of passive smoking exposure (childhood exposure
from parents, adult residential exposure and adult occupational exposure)
were considered to have the most complete exposure measures.

For all studies combined, long-term second-hand smoke exposure was
associated with a 27 percent increase in breast cancer risk among women who
were lifetime non smokers. The quality of the second-hand smoke exposure
history best differentiated those studies that suggest increased risk from
those that do not. In the subset of 5 studies with the best exposure
assessment, the breast cancer risk was increased by 90 percent, but was only
elevated 8 percent for the remaining studies with poorer second-hand smoke

Overall, premenopausal breast cancer risk was elevated 68 percent with
passive smoking among life-long non-smokers. The premenopausal risk was up
119 percent for the 5 studies with more complete second-hand smoke measures.

Cigarette smoke mutagens have been reported in the breast fluid of
non-lactating women, and nicotine has been found in greater concentrations
in the breast fluid of smokers than in the plasma. Animal studies
demonstrate that mammary tumours in rats, mice and/or hamsters can be
induced by a number of tobacco smoke carcinogens.

For women who had smoked, the breast cancer risk estimate was increased by
46 percent when compared to women with neither active nor regular passive
smoke exposure. Active smoking was associated with a 108 percent increase in
breast cancer risk, in those studies with better second-hand smoke measures.
Studies exploring biological mechanisms are needed to explain the
unexpectedly high passive and active smoking risks, as well as their

Dr. Johnson concludes, "this analysis of breast cancer risk finds that
studies with comprehensive passive exposure assessment suggest that both
passive and active smoking are risk factors for premenopausal breast

Article: "Accumulating Evidence on Passive and Active Smoking and Breast
Cancer Risk," Kenneth C. Johnson, International Journal of Cancer; Published
Online: May 31, 2005 (DOI: 10.1002/ijc.21150).