The researchers focused on three SNPs -- on chromosomes 12p11, 12q24 and 21q21.
Easton's team found that the variant on the 12p11 chromosome is linked with both estrogen receptor-positive breast cancer (which needs estrogen to grow) and estrogen receptor-negative breast cancer. The other two variants are only linked with ER-positive cancers, they said.
One of the newly identified variants is in an area with a gene that has a role in the development of mammary glands and bones. Easton said it was already known that mammary gland development in puberty is an important period in terms of determining later cancer risk. "But these are the first susceptibility genes to be shown to be involved in this process," he said.
One of the other SNPs is in an area that can affect estrogen receptor signaling, the researchers found.
Melner, noting some of the research is "fine tuning" of other work, said in his view the new understanding of the signaling pathways and their genetic links is the most important finding.
"When you delineate a pathway, you bring up new potential targets for therapy," he said. "The more targets you have, you open up the potential for having multiple drugs and attacking a cancer more easily, without it becoming more resistant."
Overall, Melner added, the results underscore the complexity of the different mechanisms involved in breast cancer development.
For more about the genetics of breast cancer, visit the American Cancer Society.
SOURCES: Douglas Easton, Ph.D., professor, genetic epidemiology, University of Cambridge, England; Michael H. Melner, Ph.D., scientific program dir
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