Parents who smoke are putting their daughters at increased risk of breast
cancer, according to an expert panel that has unanimously agreed strong enough
evidence now exists to link second-hand smoke to breast cancer.
"Even moderate exposure to passive smoking, such as living or working with a
smoker early in life, increases a woman's risk of breast cancer when she is in
her 30s, 40s and 50s," panellist and University of Toronto public health expert
Dr. Anthony Miller says.
"That is very important information people should know."
Studies on the possible relationship between cigarette smoke and breast cancer
have been inconsistent, with some showing an increase in risk and others not.
But after reviewing all available evidence — more than 100 studies — the panel
concluded that all women who smoke, particularly young women, are at increased
risk of breast cancer, and that even young women who don't smoke are at
increased risk if they're exposed to second-hand smoke.
"An estimated 80 to 90 per cent of women have been exposed to tobacco smoke in
adolescence and adulthood," says panel chairman Neil Collishaw, of Physicians
for a Smoke-Free Canada. "Those women face an increased risk of breast cancer
because of that exposure."
"Everyone needs to know that no girls and no women should be exposed to tobacco
smoke," Miller said.
According to the 11-member Canadian expert panel on tobacco smoke and breast
cancer risk:
- Smoking increases the risk of breast cancer in all women. "On average, it
would be about a 50- to 70-per-cent increase in risk, depending on how much
women smoke," says Miller, associate director of research at the University of
Toronto's Dalla Lana School of Public Health.
One in seven women in Canada will develop breast cancer in their lifetime. "If
you're an active smoker, you've moved from one in seven, to about one in five,"
Miller says. The highest risks were for women who started to smoke before age
15.
One study of women who carry the genes associated with breast cancer found those
who smoked more than one pack a day for five years had double the risk of breast
cancer than non-smokers.
- Exposure to second-hand smoke increases the risk of breast cancer in younger,
primarily pre-menopausal women by 40 to 50 per cent.
- There's not enough evidence to judge whether second-hand smoke increases the
risk of breast cancer in older women. But Miller says it doesn't make a lot of
biological sense to think passive smoking only increases risk in pre-menopausal
women.
- More research is needed to know how many cases of breast cancer, and deaths,
can be attributed to active and passive smoking.
But, according to the panel, "young women in particular should understand that
available evidence suggests that the relationship between breast cancer and both
active smoking and SHS (second-hand smoking) is consistent with causality.
"The public health implications of these findings highlight the need for
effective messaging."
Breast cancer is the most commonly diagnosed cancer in Canadian women, with
22,700 new cases expected this year and 5,400 deaths from the disease.
Overall, an estimated 5.9 million people, or 22 per cent of the Canadian
population aged 12 and older, were smokers in 2005, according to Statistics
Canada. Although they've fallen, smoking rates were still highest among both men
and women in the 18 to 34 age group. One-third of men and 26 per cent of women
in that age group were smokers in 2005.
There are at least 20 known or suspected cancer-causing chemicals in tobacco
smoke that have been shown to cause breast tumours in rodents. Miller says some
are even more abundant in sidestream smoke — the smoke produced by a burning,
idling cigarette. "That's the smoke you don't actively inhale if you're a
smoker, but the smoke you do inhale if you are exposed to a smoker.
"Any woman who has lived in a family where mother and/or father have smoked
throughout her life is definitely at increased risk of breast cancer," Miller
says. "She's had long-term exposure under circumstances where her breasts have
been developing, and where they are very susceptible to the effects of
carcinogens. That's the worst type of exposure."
Girls who expose themselves to their friends' smoking, especially in closed
rooms, are "probably increasing their risk of breast cancer," Miller says.
The panel, comprised of six Canadian and Five American experts, was convened by
the Ontario Tobacco Research Unit, an affiliate of the Dalla Lana School of
Public Health, with support from the Public Health Agency of Canada and the
Canadian Partnership Against Cancer.
Source : Canwest News Service
