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TUESDAY, Jan. 8 (HealthDay News) -- Not all carriers of the BRCA1 and BRCA2 genetic mutations show the same risk for developing breast cancer.
In fact, a new study finds wide variation in risk among families carrying the mutations, indicating that the mutations are influenced by other genetic, and possibly environmental, factors.
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"Risk among carriers varies considerably, and, if you accept that that's the case, there must be a reason why it varies, and the most plausible explanation is that there are other genetic factors affecting breast cancer risk that are being passed on through these families," said study author Colin Begg, chairman of the department of epidemiology and biostatistics at Memorial Sloan-Kettering Cancer Center in New York City.
And that's where more work needs to be done, said Begg, whose report was published in the Jan. 9/16 issue of the Journal of the American Medical Association.
"They're saying that not all BRCA mutations are created equal," added Dr. Len Lichtenfeld, deputy chief medical officer at the American Cancer Society.
It is known that the BRCA1 and BRCA2 gene mutations raise a woman's risk for developing breast cancer, so the degree of that risk is critical in helping a woman make choices about prevention.
But most previous studies have only looked at overall risk among mutation carriers, not individual risk or risk in specific groups.
"To some extent, people have traditionally perceived the risk as being a fixed thing," Begg said. "People have studied BRCA1 and 2 separately, but, other than that, there's the sense that if you're a carrier, you have a certain risk, and it's a high risk, and that's it."
Experts have hypothesized that there is variation in the risk of breast cancer in general due to other, as yet unknown, genetic factors, but there's scant evidence of such a variation. There has been no research on whether such variation exists among BRCA mutation carriers.
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