researchers have suspected for decades that some human cancers might be related
to things that happen to us before we are born. Specifically, they hypothesized
that women exposed to high levels of hormones when their mothers were pregnant
might have a higher risk for breast cancer as adults. A number of scientists
have attempted to prove this idea, but their results were variable. Some found
a link. Others didn't. But a new review of historical medical data suggests
that there may, indeed, be a connection.
Isabel dos Santos Silva says it's a difficult hypothesis to study. "In an
ideal world, what we would like is to be able to measure hormonal levels from
pregnancy, then measure the baby when the baby is born and have measures of the
birth size of the baby and then wait 50 or 60 years until the women reach the
ages at which incidence of breast cancer is high," she says.
that's impractical, dos Santos Silva says the next best way to test this idea
is to get historical data from many, many women. She and colleagues from the London School of Tropical Medicine
and Hygiene pooled the data from many studies of older women with breast cancer
and looked at the women's birth records. She had information from close to
600,000 women. More than 22,000 of them had developed breast cancer.
showed that women who were heavy at birth, or who were long, or who had a large
head circumference, had an increased risk of breast cancer," she says.
"So, for instance, women who were 51 centimeters long or more had about a
70 percent increased risk compared with women who were less than 49 centimeters
when they were born."
Santos Silva says she's not sure why heavier and longer women grew up to have a
greater risk of breast cancer. One hypothesis is that size reflects something
in the uterine environment, perhaps that larger babies are exposed to more of
the female hormone estrogen.
we don't know. We need more biological studies to look at underlying mechanisms
behind these associations," she says. "Another possible explanation's
that somehow the babies who are bigger, who have a larger number of stem cells
- you know the stem cells are kind of the mother of all cells - and maybe they
have them in a larger number in the breast gland.
if there are a larger number of such cells, it makes them more likely to suffer
a malignant transformation later in life. It just increases the likelihood of
Santos Silva says this additional risk is not a reason for women to become
frightened if they were big babies. She says the additional risk influences
about one case of breast cancer out of every 20. She says she and her colleagues will continue to study this
phenomenon to pinpoint the extent of the risk and to understand better what
women can do to reduce their risk for breast cancer.
Santos Silva's research was published in the online journal PLoS Medicine.