Weight gain following breast cancer diagnosis may not confer additional risk of recurrence, survival.
It has been well established that obesity prior to the diagnosis of breast cancer increases the risk of recurrence and poor survival. A new study confirms this and also suggests that weight gain following the diagnosis does not result in additional risk.
“There has been quite a bit of research looking at the effect of weight on the incidence and prognosis of breast cancer,” says lead author Bette J. Caan, DrPH, senior research scientist in the Division of Research at Kaiser Permanente Medical Program of Northern California in Oakland. “The question of what happens if one changes their weight after diagnosis has not been subjected to as much study. Because we have a group of women being actively followed, we have been able to look at what happens after diagnosis.”
The group prospectively looked at 1,692 breast cancer survivors from the Kaiser Permanente Northern California (KPNC) Cancer Registry, the Utah Cancer Registry, and a group who had declined participating in the Woman’s Healthy Eating and Living (WHEL) trial. Data was gathered on pre-diagnosis weight, weight at study entry, and height; from this, weight change and body mass index (BMI) were calculated. Approximately 7 years of follow-up was included.
“People jumped to the assumption with little data that if weight at diagnosis reduces survival and increases the risk of recurrence, then it follows that gaining more weight after diagnosis should be equally as bad,” says Caan. “We wanted to see what effect weight gain really had.”
Obesity 1 year prior to diagnosis was associated with an increased risk of death from any cause and a suggestion of increased risk of death from breast cancer. However, weight gain up to 4 years following diagnosis was not linked to an increase in death or recurrence.
“Because the confidence interval for the increased risk of death from breast cancer crossed 1, we are only able to say that there is a suggestion in this case,” says Caan. “Even though the point estimate shows a 60% increase in risk, we have to acknowledge that it did not meet the test for statistical significance. Since death from breast cancer is a proportion of total deaths, this may be an indication that the study was not powered sufficiently to find differences if they existed.”
Moderate weight loss (5% to 10%) was not found to decrease risk for death or reappearance of the disease. In addition, weight loss greater than 10% between pre-diagnosis and the end of the study period saw an increase in risk of recurrence and any cause death compared to having stable weight.
“We confirmed others’ findings that weight at diagnosis does increase risk of recurrence and poorer survival,” says Caan. “When we looked at weight gain for the first 4 years after diagnosis, we did not find that it conferred any additional risk. Losing weight did not change the risks either.”
This led them to say that the weight at diagnosis is more important because that probably represents a person’s habitual weight pattern over their adult life span. The weight that happens after the diagnosis is confirmed may be in response to treatment or the side effects, such as a quicker onset of menopause.
“Clinically, it is unclear that changing a woman’s weight following a breast cancer diagnosis is going to have much of an effect on their risk for recurrence or death from breast cancer,” Caan says. “We don’t want to suggest that if they are overweight they shouldn’t lose weight, because there are other health risks that weight reduction would help. But we also don’t want to suggest that losing weight is going to change a woman’s risk of having a recurrence or dying from breast cancer.”
Julie Gralow, MD, director of breast medical oncology at the University of Washington and Fred Hutchinson Cancer Research Center in Seattle, is not sure that this particular study is “the definitive word that weight changes following diagnosis mean nothing.”
“When you start breaking the data down to major events, some of the numbers become quite small,” Gralow said. “While they started with 1,692 survivors, by the time you broke it down to those who had a recurrence, then what percent of them had gained weight versus not, you start to get some pretty small numbers of events.”
Another concern is the timing of the weight measurement. One weight was the year before diagnosis, and another was measured on admission to the study. On average, they were enrolled approximately 2 years after diagnosis.
“This is a pretty short time point for weight gain,” says Gralow. “Most of my women consistently gain a few pounds a year so that by the time they are 10 years out, there is a lot more weight gain than you would find in the first couple of years. I am not sure the study is able to address that kind of patient.”
Gralow, who was not involved in the study, also noted that this trial was observational and not a focused weight loss intervention. Because of this, there was no way to know why or how the women who lost weight did so (could have been due to health issues in some cases and not intentional). This study was not designed to test whether intentional weight loss in overweight/obese women with a breast cancer diagnosis improves outcome.
“These results do not give us a lot of guidance either way on the discussion of weight loss with our patients in the context of recurrence or survival,” Gralow continues. “It is not definitive in telling us that eating well, engaging in physical activity, and maintaining a good body weight doesn’t matter.”
Caan BJ, et al. Pre-diagnosis body mass index, post-diagnosis weight change, and prognosis among women with early stage breast cancer. Cancer Causes Control. 2008 Aug 28. [Epub ahead of print] DOI 10.1007/s10552-008-9203-0
Kurt Ullman is a veteran freelance health and medical writer based out of Indianapolis.