Breast
Cancer Survival May Be Improved by Exercise
Women who are physically active in the year before
they receive a diagnosis of breast cancer are more likely to survive
the disease, according to a study reported in the journal Cancer.
" 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," says study author Page Abrahamson, Ph.D., at the Fred Hutchinson
Cancer Research Center in Seattle. In the study, Dr. Abrahamson's team analyzed data
on nearly 1,300 women ages 20 to 54 who were diagnosed with invasive
breast cancer between 1990 and 1992.
The researchers asked the study participants about
their average frequency of moderate and vigorous physical activity
when they were ages 13, 20, and during the year before their diagnosis.
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 rated in the highest 25 percent,
in terms of their level of activity, were 21 percent 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 percent 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, according to the researchers.
"We were not able to evaluate detailed, long-term
exercise," notes Dr. Abrahamson. "However, exercise levels in the year
before diagnosis is likely an indicator of a person's average adult
exercise patterns."
While many other researchers have 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.
One previous study found a beneficial effect of
exercise for both ideal-weight women and overweight women diagnosed
with breast cancer, explains Dr. Abrahamson.
Exactly why this study did not show much benefit
for normal-weight women is not known, she says.
"This is difficult to explain,” she says. “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, Dr.
Abrahamson says.
"Once women receive radiation or chemotherapy after
diagnosis, they no longer produce hormones from their ovaries,” she
explains. “Therefore, lower-weight women wouldn't necessarily
gain extra benefit from exercise.”
"However, for overweight women, they are still getting
hormones from their excess fat tissue and are at a higher risk of dying,” she
says.
“It is possible that overweight women who
are exercising are lowering their hormone levels through exercise and
increasing their odds of surviving, explains Dr. Abrahamson. "Previous
studies have shown exercise to significantly decrease estrogen levels
in overweight women."
An expert at the American
Cancer Society, Alpa Patel, Ph.D., says this study adds another
piece to the puzzle.
Dr. Patel, director of the Cancer Prevention
Study-3, remarks that, "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 adds, 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, Ph.D., at the University of Southern
California's Keck School of Medicine, says "the study suffers from
the problem that the activity refers to only activity prior to diagnosis
of breast cancer," 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, Dr. Bernstein says exercise certainly cannot
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 says.
Always consult your physician for more information.
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