Women who have survived breast cancer are at greater risk of recurrence and death if they gain a lot of weight following their diagnosis, according to a new study.
However, gaining only a moderate amount of weight does not pose such a risk, the researchers say.
"A lot of women are fearful that if they gain weight , it's going to increase their risk" of recurrence and death, said study researcher Bette Caan, of Kaiser Permanente Division of Research in Oakland, Calif. But "small amounts of weight gain should not be worrisome," Caan said.
The researchers also found most women are not gaining large amounts of weight after their breast cancer diagnosis. But the ones who do are more likely to be normal weight than overweight at their diagnosis.
More research is needed to determine what makes certain women prone to gaining a lot of weight after their diagnosis, Caan said.
The study will be presented this week at the American Association for Cancer Research meeting in Orlando, Fla.
Previous work has found that women who are overweight or obese at the time of their breast cancer diagnosis are less likely to survive than those who are normal weight. However, less is known about the risk to women who gain weight after their diagnosis.
Caan and her colleagues followed 18,336 women who had been diagnosed with breast cancer between 1976 and 2006, but their cancer went into remission. Participants' weight and body mass index (BMI), or a measure of fatness based on a height-weight ratio, were assessed on average two years after their original breast cancer diagnosis.
Women whose weight increased by 10 percent or more during this period were 14 percent more likely to have a recurrence of breast cancer compared with those whose weight remained stable. This means a 150-pound (68 kilograms) woman would need to gain 15 pounds (6.8 kg) over a two-year period to fall into the at-risk group. Only about 16 percent of women fell into this group, and they were also at an increased risk of death.
Women who experienced a moderate weight gain (5 to 10 percent increase compared with their weight before diagnosis) were not at increased risk for recurrence or death, the researchers say.
Almost 60 percent of women stayed within 5 percent of their original weight, Caan said.
The researchers aren't sure why a large weight gain following a breast cancer diagnosis is linked to worse outcomes. But it could be because fat, especially around the abdomen, is easily converted into the hormone estrogen, Caan said. Estrogen is known to promote the growth of breast cancer cells.
In addition, weight gain is known to increase inflammation in the body, which may play a role in a patient's risk of recurrence or death, Caan said.
Pass it on: Gaining large amounts of weight after a breast cancer diagnosis may increase the risk of recurrence and death among those whose cancer has gone into remission.
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Rachael is a Live Science contributor, and was a former channel editor and senior writer for Live Science between 2010 and 2022. She has a master's degree in journalism from New York University's Science, Health and Environmental Reporting Program. She also holds a B.S. in molecular biology and an M.S. in biology from the University of California, San Diego. Her work has appeared in Scienceline, The Washington Post and Scientific American.