Lifestyle Factors as Predictors of Cancer in Women
A prospective trial in which 13,388 women at high risk for breast cancer were randomly assigned to receive either prophylactic tamoxifen (20 mg per day for 5 years) or placebo has shed new light on site-specific cancer incidences related to three lifestyle factors: cigarette smoking, physical activity, and alcohol consumption (Abstract 1505). Baseline lifestyle factors were self-reported, and no provision was made for changes in lifestyle during the study. The trial, presented by Stephanie R. Land, PhD, of the University of Pittsburgh Cancer Institute, was part of the Breast Cancer Prevention Trial of the National Surgical Adjuvant Breast and Bowel Project. Dr. Land spoke at the Cancer Prevention and Epidemiology Oral Abstract Session.
Candidacy for this study required that individuals be age 35 or older (67% of women were postmenopausal) with no history of breast cancer. During the study, participants were required to undergo twice-yearly physical exams and annual mammograms. Documentation of all cancer events and hospitalizations was centrally reviewed. After a median follow-up of 7 years, with 13,208 evaluable participants, 395 cases of invasive breast cancer, 66 cases of lung cancer, 35 cases of colon cancer, and 74 cases of endometrial cancer had occurred. The data analysis did not include consideration of cancer events in the tamoxifen and control groups.
Using the 55% of women who had never smoked as the reference group, the study demonstrated a linear increase in risk for breast cancer for women who had smoked for 15 to 35 years (34%) or for more than 35 years (59%). The overall risk of breast cancer from smoking was significant (p = 0.007). In contrast to other studies of smoking in cancer causation that use pack-years as the measure of exposure, this study used only duration of smoking even though data were collected regarding age at starting to smoke, current smoking frequency and intensity, past intensity, and age at quitting in former smokers.
Not surprisingly, smoking was also shown to be a significant lifestyle factor in the incidence of lung cancer (p < 0.001). The study did not, however, distinguish among lung cancer morphologies, thus overlooking the fact that some cases might not have been smoking related, nor did it take into account the well-documented lung cancer risks from secondary smoke exposure and industrial pneumotoxins.
With respect to colorectal cancer, cigarette smoking was deemed to be a causal factor, but with significance only for those whose smoking habit exceeded 35 years (p < 0.001).
Physical Activity and Alcohol Consumption
Leisure-time physical activity was loosely stratified as inactive, light, moderate, or vigorous. It specifically excluded work-related physical demands such as walking, lifting, climbing, and vacuuming. Fifty-four percent of participants placed themselves in the lowest two categories. Their risk for endometrial cancer was significantly greater than that for individuals who exercised moderately or vigorously (p = 0.026).
At entry, participants were asked to characterize their consumption of spirits, wine, and/or beer as abstinent, moderate (one drink per day), or heavy (more than one drink per day with no differentiation of amounts above one). A drink of spirits was defined as 1.5 ounces of alcohol, beer as one 12-ounce drink, and wine as one 5-ounce drink. No correlation was found between alcohol consumption and either endometrial or lung cancer. Moderate alcohol consumption was associated with a significant 65% risk reduction for colon cancer (p = 0.019), a presumed protective effect that is unexplained.
In contrast with other studies that have shown a correlation between alcohol and breast cancer as the number of daily drinks rises from two to six, no correlation was found in this study. Dr. Land characterized this finding as “provocative,” and it was generally dismissed during the discussion period as an artifact resulting from too few participants willing to admit to more than two drinks per day.