"We found a beneficial effect on survival for exercise undertaken in the year before diagnosis, particularly among women who were overweight or obese near the time they were diagnosed with breast cancer," said study author Page Abrahamson, a postdoctoral researcher at the Fred Hutchinson Cancer Research Center in Seattle.
Abrahamson led the research while at the University of North Carolina, Chapel Hill. The study is published in the Oct. 15 issue of Cancer.
In the study, Abrahamson's team analysed data on nearly 1 300 women ages 20 to 54 who were diagnosed with invasive breast cancer between 1990 and 1992. They asked the women about their average frequency of moderate and vigorous physical activity when they were age 13, 20 and during the year before their diagnosis.
Regular exercise helped
An abundance of regular exercise before diagnosis was associated with improved disease outcomes. The association was particularly strong for women with a body mass index (BMI) of more than 25 - the statistical threshold for overweight - who also reported the highest levels of physical activity in the one year before their diagnosis. (For reference, a woman 5 feet 5 inches tall who weighs 150 pounds has a BMI of 25.)
Overall, women that rated in the highest 25% in terms of their level of activity, were 21% more likely to survive than those rated in the bottom quarter. The benefits for women with BMIs above 25 who had high levels of activity rose; they were 30% less likely to die than those with BMIs above 25 who engaged in low levels of activity.
Activity in the teen years or early adulthood did not have an impact on survival, the researchers said. "We were not able to evaluate detailed, long-term exercise," Abrahamson said. "However, exercise levels in the year before diagnosis is likely an indicator of a person's average adult exercise patterns."
While much other research has suggested that exercising regularly reduces the risk of getting breast and other cancers, less is known about what effect activity has on a woman's prognosis if and when she gets breast cancer.
A previous study
One previous study found a beneficial effect of exercise for both ideal-weight women and overweight women diagnosed with breast cancer, Abrahamson pointed out.
Exactly why this study did not show much benefit for normal-weight women isn't known, she said. "This is difficult to explain. It is possible that our finding is a fluke and that improved survival would apply to all women with breast cancer."
Another theory revolves around weight-linked differences in circulating estrogen. Exercise is known to lower estrogen levels, Abrahamson said. "Once women receive radiation or chemotherapy after diagnosis, they no longer produce hormones from their ovaries. Therefore, lower-weight women wouldn't necessarily gain extra benefit from exercise," she said.
"However, for overweight women, they are still getting hormones from their excess fat tissue and are at a higher risk of dying. It is possible that overweight women who are exercising are lowering their hormone levels through exercise and increasing their odds of surviving," the Seattle researcher said. "Previous studies have shown exercise to significantly decrease estrogen levels in overweight women."
Exercise before diagnosis may help
"This study adds another piece to the puzzle," said Alpa Patel, director of the Cancer Prevention Study-3 for the American Cancer Society, in Atlanta. "We know that lifelong physical activity reduces the risk of breast cancer, and some studies show even initiating the exercise in adulthood reduces risk."
Now, she added, this study shows that physical activity before a diagnosis of breast cancer may help women survive. Another expert said the study does have its flaws. Leslie Bernstein, professor and chair of cancer research at the University of Southern California's Keck School of Medicine, said "the study suffers from the problem that the activity refers to only activity prior to diagnosis of beast cancer," she said, rather than lifetime activity.
"When we looked at this same issue in a similar design, but with measures of activity across the lifespan up to the date of diagnosis, we saw no impact of exercise activity on the risk of dying or overall mortality. Still, exercise certainly can't hurt, and may help."
"I would recommend that women with breast cancer begin to participate in an exercise program, one that is carefully considered by their physicians, considering any [other diseases] they might have," she said. -(HealthDayNews, September 2006)