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 The cancer risk rises with greater weight, researchers found, and
women with the most severe obesity were 86 percent more likely to
develop the most common form of breast cancer, and to be diagnosed
with more advanced cancers.
While other research has pointed to a link between excess weight and
breast cancer risk, it's important to confirm that link, especially
for something changeable like weight, "because that suggests women
can do something about it," said Marian Neuhouser, of the Cancer
Prevention Program at the Fred Hutchinson Cancer Research Center in
Seattle, who led the study.
For the new study, published in JAMA Oncology, the researchers
analyzed data from the large, long-term Women's Health Initiative
study.
They looked at data on 67,142 post-menopausal women ages 50 to 79
years old from across the U.S., and followed them for an average of
13 years. Overall, there were 3,388 breast cancers detected by 2010.
The study team grouped women by their body mass index (BMI), a
measure of weight in relation to height. A BMI of less than 25 is
considered normal, BMI between 25 and 30 is considered overweight
and over 30 is obese. A BMI of 35 - the equivalent of a five-foot
six-inch person weighing 216 pounds - or above is considered
severely obese.
About 5 percent of women in each weight group were diagnosed with an
invasive breast cancer during the study period, but the risk of
breast cancer increased with weight.
Women with BMIs of 35 and up were about 56 percent more likely to be
diagnosed with any type of invasive breast cancer during the study,
compared to normal-weight women.
When the researchers looked at specific breast cancer subtypes, they
found the most-obese women were 86 percent more likely than
normal-weight women to be diagnosed with breast tumors that are
fueled by the hormones estrogen and progesterone.
These so-called estrogen receptor-positive and progesterone
receptor-positive breast cancers are the most common forms of the
disease. There was no link between body weight and breast cancers
that are hormone receptor-negative.
Using hormone replacement therapy after menopause did not change the
relationship between breast cancer and weight, the researchers
found.
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The analysis did reveal that normal-weight women who gained more
than 5 percent of their starting weight over the study period had a
35 percent increased risk of breast cancer.
But for women who were already overweight or obese, losing weight
did not lower their increased breast cancer risk.
"I think it’s important to note that this was not a weight loss
trial," Neuhouser said.
A research trial looking specifically at whether weight loss
decreases breast cancer risk is needed to determine if it's helpful
for women, she said.
While more studies need to be conducted, Dr. Clifford Hudis told
Reuters Health the new results are "a caution that once you're
overweight the damage may be done."
Hudis, who co-wrote an editorial accompanying the new study, said
research also needs to find out why increased weight may increase
breast cancer risk so that solutions can be found.
His own group's research has focused on the potential role of
inflammation generated by fat tissue, and possibly other effects on
the endocrine system that could fuel cancer growth, he writes in the
editorial.
"Unfortunately (overweight and obesity) is just a growing problem in
Western countries," said Hudis, who is chief of the Breast Medicine
Service at Memorial Sloan Kettering Cancer Center in New York. "It’s
a public health challenge."
SOURCE: http://bit.ly/1HwBopw and http://bit.ly/1HwBnSt JAMA
Oncology, online June 11, 2015.
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