Women who exercise regularly are less likely to suffer a recurrence of breast cancer because exercise reduces production of estradiol, a hormone that has been found to exacerbate tumor growth. And exercise decreases insulin resistance, which also has been linked to breast cancer.
Women who are overweight are at greater risk for recurrence, so helping to maintain a healthy weight is another reason why exercise is good for breast cancer survivors.
On top of that, women who increase their physical activity after treatment for breast cancer say they have more energy and less pain, according to the American Council on Exercise.
But a recent study by researchers at the Fred Hutchinson Cancer Research Center in Seattle indicates that after five years, there is a substantial drop-off in the amount of exercise breast cancer survivors get.
The researchers followed 631 breast cancer survivors age 18 to 64 in New Mexico, Washington state and Los Angeles over 10 years.
Prior to diagnosis, 34 percent of the women met the U.S. physical activity guidelines of at least 150 minutes of moderate exercise per week or 75 minutes of vigorous exercise. After five years, the percentage of women who met the guidelines rose to 39.5. But at 10 years, only 21.4 percent of women were getting the recommended amount of exercise.
Only 8 percent of the women met the exercise guidelines throughout the entire 10 years of the study period, the researchers found.
"I think this issue of five-year survivorship is a big deal," said Jane Raymond, director of medical oncology at Allegheny General Hospital. "A lot of women think that if they make it to five years, they're home free."
That's true for a lot of cancers, Dr. Raymond said, but "unfortunately, this isn't true of breast cancers. More than half the recurrences are after five years."
It makes sense that the amount of exercise breast cancer survivors get initially would rise, Dr. Raymond said, because "patients with breast cancer have a really strong reason for sticking with it."
But as time passes, most people tend to slack off on exercise programs, she said, and at the end of the study period, the women in it were 10 years older than when it began.
But the drop-off in exercise was consistent in all the age groups they studied, the Hutchinson researchers said, so "it seems unlikely that this pattern reflects aging alone."
A little exercise can help a lot.
Women who walked 3 to 5 hours a week lowered their risk of dying from breast cancer by 50 percent, according to a 2005 study published in the Journal of the American Medical Association.
Strength training has been found to lower the risk of lymphedema -- a blockage in the lymphatic system causing a buildup of fluid and swelling -- by 35 percent. It's most commonly caused by the removal of underarm lymph nodes or damage to the lymph nodes as part of the breast cancer treatment.
Jack Kelly: email@example.com or 412-263-1476.