Surprises found in hunt for environmental links to breast cancer
By Kerry Sheridan, AFP
November 12, 2013, 12:10 am TWN
WASHINGTON -- A decade-long research effort to uncover the environmental causes of breast cancer by studying both lab animals and a group of healthy U.S. girls has turned up some surprises, scientists say.
At the center of the investigation are 1,200 school girls who do not have breast cancer, but who have already given scientists important new clues about the possible origins of the disease.
Some risk factors are well understood, including early puberty, later age of childbearing, late onset of menopause, estrogen replacement therapy, drinking alcohol and exposure to radiation.
Advances have also been made in identifying risky gene mutations, but these cases make up a small minority.
"Most of breast cancer, particularly in younger women, does not come from family histories," said Leslie Reinlib, a program director at the National Institute of Environmental Health Sciences.
"We have still got 80 percent that has got to be environmental," said Reinlib, who is part of the Breast Cancer and the Environment Research Program (BCERP) program that has received some US$70 million in funds from the U.S. government since 2003.
Some of its researchers track what is happening in the human population, while others study how carcinogens, pollutants and diet affect the development of the mammary glands and breast tumors in lab mice.
The program's primary focus is on puberty because its early onset "is probably one of the best predictors of breast cancer in women," Reinlib said.
Puberty is a time of rapid growth of the breast tissue. Research on survivors of the Hiroshima atomic bombings in Japan has shown that those exposed in puberty had a higher likelihood of developing breast cancer in adulthood.
The 1,200 U.S. girls enrolled in the study at sites in New York City, northern California and the greater Cincinnati, Ohio, area beginning in 2004, when they were between the ages of six and eight.
The aim was to measure the girls' chemical exposures through blood and urine tests, and to learn how environmental exposures affected the onset of puberty and perhaps breast cancer risk later in life.
Researchers quickly discovered that their effort to reach girls before puberty had not been entirely successful.
"By age eight, 40 percent were already in puberty," said Reinlib. "That was a surprising bit of information."
Further research has shown that the girls appear to be entering puberty six to eight months earlier than their peers did in the 1990s.
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