Oakland, Calif. — Breast cancer survivors who experience large weight gain have an increased risk of death after diagnosis, according to research scientists at the Kaiser Permanente Division of Research in Oakland, Calif.
Breast cancer survivors who experienced large weight gain (10 percent or more over their pre-diagnosis weight) were 14 percent more likely to experience a cancer recurrence compared to women whose weight remained stable (within 5 percent of pre-diagnosis weight) following diagnosis.
The study results are being presented at the American Association of Cancer Research 102nd meeting, to be held April 2-6 in Orlando, Fla.
"Most women are not gaining a large amount of weight following breast cancer diagnosis," said lead researcher Bette Caan, DrPH, a senior research scientist at the Kaiser Permanente Division of Research. "However, our analysis showed an association with poorer outcomes overall for those who do." She explained that moderate weight gain did not affect breast cancer outcomes.
"Women tend to worry about gaining weight after a breast cancer diagnosis," said Caan. "But it's actually only the larger weight gains that increase the risk of poor outcomes."
Researchers also found that women who have large weight gains after diagnosis tend to be within normal weight ranges to begin with. In addition, the post-diagnosis effect of the weight gain tends to be greater for women who were originally thinner, they explained.
Women who were leaner to begin with at diagnosis (body mass index less than 25) and who later gained 10 percent or more, had a 25 percent higher risk of cancer death and also had a higher risk of recurrence compared to women whose weight remained stable (within 5 percent of pre-diagnosis weight) following diagnosis.
Large weight gain occurred in 16 percent of women overall. Just over 19 percent of women with a BMI less than 25 fell into the large weight gain category, but only 11.1 percent of women with a BMI greater than 30 fell into that category.
Data for the study came from the After Breast Cancer Pooling Project, which includes 18,336 breast cancer survivors from four prospective cohorts — three in the United States and one in Shanghai.
Caan explained that more research is needed to identify those women most at risk for extreme weight gain and those whose weight gain puts them at risk for poor cancer outcomes.