FRIDAY, May 25, 2012 (HealthDay News) -- Women with advanced breast cancer who have higher levels of fitness during treatment tend to live longer than women with lower levels of fitness during treatment, new research finds.
Treatments for breast cancer can weaken women's heart and lung function, according to the study by researchers at Duke University Medical Center, and the impairments can linger for years after treatment has ended.
Among those with advanced breast cancer, women whose fitness level was high during treatment were more likely to survive. Median survival was 36 months among women with high levels of fitness, compared to 16 months among low-fitness patients.
What researchers don't know, however, is if helping women to improve fitness while undergoing breast cancer treatment will boost their survival. They only found an association, not a cause-and-effect link, between the two.
Exercise tolerance tests, which measure heart and lung function, are good predictors of health and longevity in people who do not have cancer, but to what extent those same tests apply to cancer patients is less understood, study author Lee Jones, an associate professor at Duke University Medical Center, said in a Duke news release.
Breast cancer treatments have reduced death rates from the disease by roughly 2.2 percent a year since 1990, but the regimens often take a toll on women's lungs, heart, blood and skeletal muscle. Compounding the problem is that during treatment and after, women are often less active and gain weight, which can also affect their heart and lung function.
In the study, researchers tested heart and lung capacity at rest and during exercise of nearly 250 women at several points during breast cancer treatment.
Overall, women with breast cancer had much worse heart and lung function than healthy women of the same age, even those who were sedentary. For some cancer patients, the decline in fitness level was severe. One-third of the women studied had a fitness level so low that it may prevent them from doing household tasks, walking up stairs or walking a half-mile.
Some breast cancer survivors' heart and lung function remained impaired for years after treatment ended, which may indicate they will never get back their pre-chemo level of fitness, researchers said.
"Fitness level may be an important biomarker of survival among cancer patients," Jones said. "But the beautiful thing about fitness is that we can improve it with exercise training. Although we currently do not know if improving fitness in cancer patients is associated with longer survival, our data provides initial evidence to pursue this question."
The study was published online May 21 in the Journal of Clinical Oncology.
The American Cancer Society provides more information on breast cancer survival rates.