In women already at high risk of breast cancer, a study has shown that lifestyle choices can affect risk further in breast, lung, colon and endometrial cancer.
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Researchers know that lifestyle choices, such as smoking, exercise, and alcohol intake, can influence a person's risk of developing various malignancies, and now, new data show that some of those effects may be even greater in women already at high risk of breast cancer, compared with the general population.
Dr Stephanie Land, research associate professor of biostatistics in the Graduate School of Public Health at the University of Pittsburgh, and colleagues reached that conclusion after analysing the incidence of four major cancers – breast, lung, colon, and endometrial – and lifestyle information for 11,064 women who participated in the prospective, randomised Breast Cancer Prevention Trial and who were followed for at least three years before the trial was unblinded.
The trial, which demonstrated tamoxifen's utility in preventing breast cancer, enrolled women who had an elevated risk of breast cancer, compared with the general population.
Scientists have only recently demonstrated an association between cigarette smoking and increased risk of breast cancer, Dr Land explained. ‘And our study demonstrated larger effects than those reported from the recent studies. This might suggest that for women who are already at higher risk of breast cancer, such as the women in our trial, smoking is even more dangerous than for other women in the population.’
ASCO 2010–2011 President George Sledge reiterated the importance of the new study. ‘This trial was originally developed to look if a treatment would prevent breast cancer, but certainly one of the major outcomes of this study, as revealed by Dr Land's presentation, is the incredible importance of lifestyle factors’, he said.
‘We need to perhaps think, going forward, a little bit less about drugs in many cases, and think a great deal – a great deal – about whether or not we might be able to prevent the cancer just by simple changes in what a woman does on a day-to-day basis’, Dr Sledge said.
Behaviour increases risk
At baseline, 45.7% of the study participants reported participating in moderate to heavy leisure time activity, and 12.8% were current smokers. Additionally, 20.5% of the women reported that they drank no alcohol, 65.8% reported drinking one or fewer drinks per day, and 13.3% reported drinking more than one drink per day.
With a median follow-up of 8.7 years, 395 women in the study population had been diagnosed with breast cancer, 66 with lung cancer, 35 with colorectal cancer, and 74 with endometrial cancer.
‘Women who had smoked cigarettes for longer duration had an increased risk of invasive breast cancer, lung cancer, and colon cancer’, said Dr Land. ‘Those results were all highly statistically significant.’
Specifically, women who smoked for 15 to 35 years had a 34% increased risk of breast cancer, while women who smoked more than 35 years had a 59% increased risk. Women who smoked for more than 35 years also had a five-fold increased risk of colon cancer. Dr Land and colleagues reported no increase in colon cancer risk for women who smoked fewer than 35 years.
By contrast, a woman's lung cancer risk increased with both duration and intensity of smoking. Women who smoked less than one pack per day for 15 to 35 years had a two-fold increased risk, relative to non-smokers, whereas women who smoked one or more packs a day for the same duration had a five-fold increase in risk.
Women who smoked less than one pack a day for more than 35 years had a 13-fold increase in risk, and that increased risk soared to 30-fold for women who smoked one or more packs a day for more than 35 years.
In addition to smoking, the researchers found that alcohol and physical activity had an impact on cancer risk, which is consistent with previous studies. Women who consumed a moderate amount of alcohol, defined as one or fewer drinks per day, had a 65% decrease in colon cancer risk. However, women who consumed more than one drink a day did not appear to have any drop in risk, compared with non-drinkers.
Additionally, women who had little or no leisure time activity had a 72% increased risk of endometrial cancer. Dr Land noted that some of that elevation in risk is due to excess weight, though she did not specify what proportion of risk was due to inactivity versus weight.
Modifying behaviour to decrease risk
‘This study is good news because most of the other major factors known to cause breast, lung, colon, and endo-metrial cancer are not something women can control. But healthy lifestyle choices provide women a way to reduce their risk of these four major cancers’, Dr Land said.
The new data provide one more reason women should stop smoking, and one more reason for their doctors to encourage them to do so, Dr Sledge added. The results regarding alcohol consumption, though, are less conclusive, in his view. Previous studies have suggested that alcohol consumption may increase a woman's risk of breast cancer, but that finding was not seen in this study. Therefore, he said, more research is needed before a solid conclusion can be made.
That lack of definitive information on the impact did not lessen Dr Sledge's overall enthusiasm for Dr Land's study. ‘We still have much to learn about what causes cancer, but I think we already know what can prevent cancer in many patients. And this study is certainly a step in telling us more about that.
© 2011 Lippincott Williams & Wilkins, Inc.