New research suggests that young women who currently smoke and who have smoked one pack of cigarettes a day for 10 years or more have a much higher risk for estrogen receptor-positive breast cancer - the most common form of the disease - compared with women who have smoked for a shorter period of time.
This is according to a study recently published in the journal Cancer.
The research team, led by Dr. Christopher Li of the Fred Hutchinson Cancer Research Center in Seattle, WA, says there is quite a bit of research that has associated smoking among young women with an increased risk of breast cancer.
But they say few studies have assessed the link between smoking and subtypes of breast cancer.
For their study, the investigators analyzed 778 women who had estrogen receptor-positive breast cancer, 182 women with triple-negative breast cancer, and 938 women who were cancer-free.
When the breast cancer cells have a significant number of receptors for estrogen, this is classed as estrogen receptor-positive breast cancer. This type of cancer is more likely to respond to hormonal therapies.
Triple-negative breast cancer means the breast cancer cells are not positive to receptors for estrogen, progesterone or HER2. This form of breast cancer is usually more aggressive.
All patients were aged between 20 and 44 years, and those with breast cancer were diagnosed with the disease between 2004 and 2010.
The researchers asked the women about their smoking history. This included information on whether they have ever smoked, whether they still smoke, how much they have smoked in the past/currently smoke, and for how long they have smoked.
Risk increases by 60% with 10-year smoking history
The results of the study revealed that women who had ever smoked (more than 100 cigarettes in their lifetime) had a 30% increased risk of breast cancer overall, compared with never smokers (fewer than 100 cigarettes in their lifetime).
However, the researchers found that young women who were current or recent smokers, and who had been smoking one pack of cigarettes a day for at least a decade, were 60% more likely to develop estrogen receptor-positive breast cancer, compared with women who had smoked for fewer years and those who had a history of fewer pack-years.
The researchers found no link between smoking in young women and the risk of triple-negative breast cancer.
Commenting on the findings, the researchers say:
"The current study adds to recent evidence indicating that smoking is modestly associated with breast cancer risk in young women.
Expanding on earlier work, our findings suggest that this association is limited to an increase in the risk of estrogen receptor-positive breast cancer and that smoking does not have an impact on the risk of triple-negative breast cancer."
The researchers conclude that since there is consistently strong evidence that smoking in young women may increase the risk of breast cancer, there should be ongoing efforts to prevent young women from taking up smoking and increased awareness surrounding the risks of smoking in this population.
Medical News Today recently reported on a study suggesting that total smoking bans can effectively help smokers to cut back or quit completely.