Long-time smokers may face an increased risk of death if they develop breast cancer, according to a Japanese study that adds to a growing body of evidence highlighting the lethal effects of cigarettes.
Among more than 800 women with breast cancer, those who had smoked for more than two decades had at least triple the odds of dying of any cause, or from breast cancer in particular, compared with women who never used cigarettes.
Fewer years of smoking were also linked to an increased risk of death from breast cancer, but the extra risk was so small that it might have been due to chance.
Other studies have explored the connection between smoking and survival among breast cancer patients, but the current research is among the first to assess the impact of the duration of smoking on outcomes for women with this type of tumour, said study co-author Dr. Masaaki Kawai, a breast oncologist at Miyagi Cancer Center Hospital in Japan, in email to Reuters Health.
Worldwide, breast cancer is the most common malignancy in women. About one in nine women will eventually develop it, according to the National Institutes of Health. The risk increases with age, from 1 in 227 at age 30 to 1 in 26 by age 70. Factors such as obesity, inactivity, alcohol use or early menstruation can increase the risk.
For the current study, Kawai and colleagues followed 848 women who were treated at the Miyagi Cancer Center Hospital between 1997 and 2007 for newly diagnosed breast cancer.
Women who described themselves as current smokers were typically younger when their breast cancer was diagnosed, about 49 years old on average, compared with 53 for women who claimed to be former smokers and 58 for nonsmokers.
The current smokers also tended to weigh less, have more advanced tumours, and have fewer health complications than the other women in the study.
With half of the women in the study followed for at least seven years, the researchers saw 170 deaths from all causes - including 132 deaths from breast cancer.
Roughly one third of the women hadn't yet gone through menopause when they started the study. In this subset, those who had smoked for more than about 21 years were three times more likely to die of any cause, and nearly three and a half times more like to die of their breast cancer, than those who never used cigarettes.
Researchers also examined exposure to second-hand smoke among women whose husbands were current or former smokers and found no significant impact on the women's risk of death from any cause or from breast cancer specifically.
One limitation of the study is its reliance on patients to accurately report information about their exposure to cigarettes, the researchers acknowledge in the journal Cancer Science. The study also lacked data on second-hand smoke that didn't come from the women's spouses.
Even so, the findings add to a growing body of research pointing to the specific risks smoking poses for women with breast cancer, said Peggy Reynolds, a researcher at the Cancer Prevention Institute of California and Stanford University School of Medicine.
"There are now quite a few studies suggesting that active smokers diagnosed with breast cancer have poorer survival - not to mention accumulating evidence that smokers may have a greater risk of developing breast cancer," Reynolds, who wasn't involved in the study, said by email.
This study, however, didn't look at whether smoking causes breast cancer.
Even if not all of the evidence is conclusive, it should still be enough to motivate patients to abandon cigarettes, said Mia Gaudet, strategic director of breast and gynecologic research at the American Cancer Society in Atlanta, in an email.
"Regardless of whether or not a woman has breast cancer, quitting smoking is likely to be the best lifestyle change a woman can make to improve her health," she said.