Early puberty makes some women more likely to develop breast cancer later in life, says a study that provides new clues in the ongoing hunt for genes involved in the disease.
Those as yet unknown genes seem to make women more sensitive to the ill effect of hormones at one important time of life, puberty, explains study author Ann Hamilton, an assistant professor of preventive medicine at University of Southern California Keck School of Medicine.
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Female hormones are known to be involved in the risk of breast cancer, Hamilton says, and research has focused on the effects of lifetime exposure. The new study results indicate the hunt should also include genes that affect "this critical time period, genes that make hormones more important at that time."
Twins studied
Hamilton and another Keck faculty member, Dr Thomas Mack, made that finding with 1 811 pairs of female twins, one or both of whom had breast cancer. Some were identical twins with the same set of genes, some were fraternal twins whose genes differed slightly. They were questioned about a number of factors that could affect breast cancer risk - number of children, age when the first child was born, age of menopause, and age of puberty.
Among the 209 pairs of identical twins who both had breast cancer, the one who began puberty earlier was more than five times as likely to get breast cancer first. Indicators of puberty were first menstruation, when menstruation became regular, and breast development. The effect was strongest for the women who began menstruating before age 12, says a report in the June 5 issue of the New England Journal of Medicine.
Affected at the time of puberty
What's true for these twins is probably true for some other women, Hamilton says. "Women with this particular genetic susceptibility are affected at the time of puberty," she says. "And the gene-environment interaction is strongest when puberty occurs earlier."
A couple of genes, designated BRCA1 and BRCA2, are known to increase the risk of breast cancer, Hamilton says, but there are a number of reasons to believe they are not responsible for the puberty effect.
Hamilton and Mack have begun to study possible genetic factors in the twins, a study that promises to be a long one, she says.
Shade of doubt
The study is "very provocative, something that should be followed up," says Patricia Hartge, deputy director of the epidemiology and biostatistics programme at the American National Cancer Institute, who wrote an accompanying editorial.
There is room for a shade of doubt, because the number of women in the study was relatively small, Hartge says, but she believes "the puberty finding will hold up."
It was an ingenious idea to study twins, Hartge says. "They understood that if you have identical twins and they both develop breast cancer, they probably have some of the genes we are looking for."
Now comes the hard part, Hartge says: finding the genes. "We don't know what those genes are," she says. "In the next stage of research, we want them to be identified." - (HealthScout News)
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