|
 Researchers examined data on more than 18,000 women with breast
malignancies and 184,000 women the same age without breast cancer.
They found breast density appeared to be the biggest indicator of
cancer risk, even more than other common risk factors like family
history or waiting until after age 30 to have babies.
“Women with dense breasts have a roughly 2-fold higher breast cancer
risk relative to women with non-dense breasts,” said lead study
author Dr. Natalie Engmann of the University of California, San
Francisco.
This is a problem because 60 percent of younger women have dense
breasts and so do 40 percent of older women who have gone through
menopause – and because dense breasts make tumors harder to detect
on mammograms, Engmann said.
“Our findings suggest that because breast density is a strong,
common risk factor that can be modified, reducing the number of
women with dense breasts may prevent a substantial proportion of
breast cancer cases,” Engmann added by email.
The results don’t mean that breast density would be the most
meaningful risk factor for every woman, however. Rather, from an
epidemiology standpoint they explain many cancer cases in the
general population because so many women have dense breasts.
In the study, researchers examined data on women with four
categories of breast density: almost entirely fat, mostly fat with
some dense tissue, moderately dense and predominantly dense.
Then, they looked at several known breast cancer risk factors:
women’s weight, family history of the disease, personal history of
benign biopsy results, breast density and having a first baby after
age 30.
About 39 percent of breast cancer cases before menopause and 26
percent of cases afterwards might be prevented if women in the two
highest breast-density categories had less dense breast tissue, the
study team calculated.
There isn’t much women can do to reduce breast density, the authors
acknowledge. One drug, tamoxifen, reduces cancer risk and breast
density but it has serious side effects and generally isn’t
recommended to women unless they have a high risk of cancer.
Gaining weight tends to add fatty tissue to the breasts and lower
density, but obesity is independently tied to an elevated risk of
breast cancer in older women, the study also found.
In fact, roughly 23 percent of breast cancers in older women might
be prevented if overweight or obese women shed enough pounds to
achieve a healthy weight, the researchers also calculated.
[to top of second column] |
Still, compared to breast density or obesity, some other common risk
factors didn’t appear to explain as many cancer cases in the general
population. Family history was linked to about 9 percent of cases
for younger women and 8 percent in older women, for example, while
delayed childbirth was tied to 9 percent of cases for younger women
and 5 percent for older women.
One limitation of the study is that it didn’t look at certain risk
factors like genetic mutations that can greatly increase the odds of
breast cancer for individual women, the authors note.
Only 5 percent to 10 percent of breast cancers diagnosed in the U.S.
are due to inherited gene mutations linked to breast cancer,
according to the National Cancer Institute (NCI). Women with these
mutations, however, are much more likely to develop cancer, and to
have aggressive tumors that are hard to treat.
It’s unclear that women can do anything to reduce breast density,
but it may make sense for them to consider screening alternatives to
mammograms, said Dr. Christine Berg, a NCI researcher who wasn’t
involved in the study.
“I think it makes more sense for a woman with dense breasts,
particularly with other risk factors, to discuss with her doctor and
the radiologist whether or not she would benefit from other types of
screening such as MRI,” Berg said by email. “Breast tomosynthesis is
an emerging technology which I think is better than standard
mammography.”
Berg also recommended a calculator (here: http://bit.ly/2knIYuH)
developed by the Breast Cancer Surveillance Consortium for women to
assess their individual risk.
SOURCE: http://bit.ly/2k4en9u JAMA Oncology, online February 2,
2017.
[© 2017 Thomson Reuters. All rights
reserved.] Copyright 2017 Reuters. All rights reserved. This material may not be published,
broadcast, rewritten or redistributed. |
