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A major new prospective study funded by Breast Cancer Now has found that smoking is associated with an increased risk of breast cancer, particularly among those who began smoking during adolescence and those with a family history of the disease.
It has been thought for some time that smoking might increase breast cancer risk, with a number of plausible biological reasons being suggested due to the carcinogenic effects of tobacco smoke – but previous epidemiological studies have produced inconsistent evidence into the link between the two.
However, a new analysis of 102,927 women from the Breast Cancer Now Generations Study – one of the world’s largest prospective cohort studies into the causes of breast cancer, which is following more than 113,000 UK women for 40 years – found that smoking was associated with an increase in breast cancer risk.
The findings – published today in Breast Cancer Research – may also have particularly important implications for women already at an increased risk of breast cancer due to having a family history of the disease.
The study found that female smokers with a family history of breast cancer were around 35% more likely to develop the disease than someone with a family history who had never smoked.
Higher risk of cancer with younger smokers
Scientists at The Institute of Cancer Research, London, established participants’ smoking history through questionnaires at their recruitment to the study and during follow-up, from 2003 onwards. They determined whether they had ever smoked, how regularly and how many cigarettes per day, and the age at which they started and stopped.
The study followed the participants for an average of over seven years, collecting further data to enable the researchers to adjust for any changes or any confounding risk factors, in particular, alcohol consumption, which itself is associated with breast cancer risk and smoking.
The new analysis – led by Professor Anthony Swerdlow and Dr Michael Jones at the ICR – observed that 1,815 out of the 102,927 women went on to develop the disease, finding that women who had ever smoked were about 14% more likely to go on to develop breast cancer than those who had not.
The study also demonstrated that the younger a woman was when she began smoking, the higher her risk of developing the disease. Those who began smoking before the age of 17 were found to be at around a 24% increased risk of developing the disease, while those who started smoking between the ages of 17 and 19 had an increased risk by about 15%.
The scientists also analysed the impact of smoking duration, and found that smoking for more than ten years had a relative risk increase of around 21%, while those who smoked for more than 30 years had an increased risk of breast cancer of around 22%, compared with women who had never smoked.
The study also identified that a woman’s risk might remain increased for at least 20 years after quitting, with those who hadn’t smoked for 1-9 years retaining about a 28% increase in breast cancer risk, and for 10-19 years around a 21% increase, compared with a woman who had never smoked.
The findings add to evidence that breast cancer may be another hazard of smoking, beyond those more widely known. There are many important health benefits from not smoking, or stopping smoking as soon as possible, even if you’ve previously smoked for a long time.
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Biological implications of smoking
According to Public Health England, regardless of how long you’ve smoked, those who quit smoking see their risk of lung cancer fall to half that of a smoker after ten years, with their risk of a heart attack falling to the same as someone who has never smoked with 15 years.
The findings add to the need for investigation into the biological implications of smoking at a young age, at a susceptible period of breast development.
Study leader Anthony Swerdlow, Professor of Epidemiology at the ICR, said:
“Our large-scale study of more than 100,000 women adds to evidence that smoking is associated with the risk of breast cancer. We particularly found an association in women with a family history of breast cancer, and women who started smoking before the age of 17.
“It is difficult to separate the effect of smoking on breast cancer because many women who smoke also drink alcohol, which is a known risk factor for the disease, and there remains uncertainty on the extent to which smoking itself is responsible.
“There are already extremely strong health reasons not to smoke. However, the data on breast cancer add a further factor for women, especially those who are young, to take into account.”
'Illuminating study'
Baroness Delyth Morgan, Chief Executive at Breast Cancer Now, which funded the study, said:
“This illuminating study adds to growing evidence that smoking may increase a woman’s chances of developing breast cancer later in life.
“Smoking remains the largest preventable cause of many cancers, as well as heart disease, and can have a devastating impact on our health. We’d strongly encourage all women and men not to smoke for the benefit of their health and wellbeing.
“For now, the Breast Cancer Now Generations Study findings suggest that avoiding smoking could be particularly important for adolescents and women with a family history of breast cancer.
“Breast cancer incidence continues to rise, and, as well as tackling smoking, we need to do much more to empower women and men to reduce their risk.
“There is no single cause of the disease, but there are some factors that we can control: it’s vital all women know that they can actively lower their risk of breast cancer by reducing their alcohol intake, being more physically active and maintaining a healthy weight.”
Reducing the risk of developing cancer
Annie Belasco, a 33-year-old mother of two young children from Windsor, was diagnosed with primary breast cancer in 2009, when she was just 25. After finishing her active treatment, Annie made a number of changes to her lifestyle to improve her health, including giving up smoking and reducing her alcohol intake.
She is now encouraging other women and men to do the same, to help reduce their own risk of developing cancer.
“For me, research like this is so important in helping women and men understand the long-term health implications of smoking. Of course, it’s impossible to know what caused my diagnosis, but I know that there’s no way I could have gone on living the way I was, smoking and drinking so excessively.
“I strongly feel that there’s not enough information for young women about the importance of healthy lifestyles, and believe it should be normal for us all to consider the impact that smoking and drinking can have later on in life.
“We need to learn to love our bodies on the inside, and for me, if speaking out about my experience of breast cancer helps even a few women change the way they live and to reduce their risk of the disease, then I couldn’t be happier.”
Smoking is a major cause of lung cancer and other cancers, as well as heart disease – all women and men are strongly advised not to smoke by health professionals, the government and health charities.
Visit the NHS Choices website for information and advice on stopping smoking or contact your doctor.