|
 But the 80 percent-higher breast cancer risk is not as scary as it
first sounds because "fortunately, breast cancer is uncommon in
young women," chief author Dr. Hazel Nichols told Reuters Health in
a telephone interview.
Nichols and colleagues found that the breast cancer risk peaks 4.6
years after a woman's most recent birth but then begins to fall.
After another 19 years, the risk returns to the same level as a
woman who has never given birth. And from there, it continues to
drop.
By 34.5 years after birth of the youngest child, the breast cancer
risk is 23 percent lower than the risk in women who had never been
pregnant.
While a 45-year-old woman who had never given birth had a 0.62
percent chance of being diagnosed with breast cancer up to that
point in her life, the breast cancer odds for a woman of the same
age who had given birth in the past three to seven years were only
slightly higher, at 0.66 percent.
Similarly, by age 50, the odds of being diagnosed with breast cancer
were 1.95 percent for the childless women and 2.20 percent for women
with a recent pregnancy, a difference of only one quarter of a
percentage point.
Women who had given birth to their first child before age 25 did not
have any elevated risk at all.
"This should not dictate when women decide to have their children
because while we are seeing this extra risk after childbirth, this
is a period of time when risk overall is exceptionally low," said
Nichols. "This is not translating to a large number of additional
breast cancers."
Mia Gaudet, scientific director for epidemiology research at the
American Cancer Society, agreed. The findings "shouldn't change
women's behavior with regard to when a woman decides to have a first
child," Gaudet told Reuters Health in a telephone interview.
"It may perhaps change how and when a woman begins to be screened
for breast cancer," added Gaudet, who was not involved in the study.
The conventional wisdom has been that pregnancy and childbirth
protect women from breast cancer, but that belief had come from
looking at the cancer rates among women age 60 and older. In fact,
half of women with breast cancer are diagnosed before age 62.
[to top of second column] |
The new findings, reported in the Annals of Internal Medicine, come
from combining data from 15 studies of nearly 890,000 women of
varying ages across three continents. They confirm what smaller
studies have suggested.
With the aggregated data, "we got a rich picture not only of when
women have their children but whether they had a family history of
breast cancer, whether they breastfed their children, and the type
of cancer that developed," said Nichols. "We are not the first to
see the short-term increase in risk after childbirth, but we are now
able to see whether or not other factors like breastfeeding your
children make a difference. When it came to breastfeeding, it did
not."
But Gaudet of the Cancer Society said the breastfeeding conclusion
is questionable because the Nichols study only looked at whether
breastfeeding ever occurred.
That's important because "prior studies have shown that it's the
duration of breastfeeding, not whether they ever breast fed or not"
that's key, she said. Those studies show that breastfeeding lowers
the breast cancer risk.
The Nichols team also found that women with the most children and
those who had children later in life had highest risks.
Having a family history of breast cancer doubled the odds of a
breast tumor compared to other mothers.
The higher risk for mothers is probably due to the fact the breast
tissue divides rapidly during pregnancy, increasing the likelihood
that a copying error will be made in the genetic code, said Nichols
of UNC's Lineberger Comprehensive Cancer Center in Chapel Hill,
North Carolina.
SOURCE: http://bit.ly/2wYH0qu Annals of Internal Medicine, online
December 10, 2018.
[© 2018 Thomson Reuters. All rights
reserved.] Copyright 2018 Reuters. All rights reserved. This material may not be published,
broadcast, rewritten or redistributed.
Thompson Reuters is solely responsible for this content.
 |
