Genetic Variant Protects Some Latina Women from Breast Cancer

An international research collaboration led by UC San Francisco researchers has identified a genetic variant common in Latina women that protects against breast cancer.

The variant, a difference in just one of the three billion “letters” in the human genome known as a single-nucleotide polymorphism (SNP), originates from indigenous Americans and confers significant protection from breast cancer, particularly the more aggressive estrogen receptor-negative forms of the disease, which generally have a worse prognosis.

“The effect is quite significant,” said Elad Ziv, MD, professor of medicine and senior author of the study. “If you have one copy of this variant, which is the case for approximately 20% (the range being 10 to 25 percent) of U.S. Latinas, you are about 40 percent less likely to have breast cancer. If you have two copies, which occurs in approximately 1% of the US Latina population, the reduction in risk is on the order of 80 percent.”

Published in the October 20, 2014 issue of Nature Communications, the new study showed that women who carry the variant have breast tissue that appears less dense on mammograms. High “mammographic density” is a known risk factor for breast cancer.

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Epidemiological data have long demonstrated that Latina women are less susceptible to breast cancer than women of other ethnicities. According to National Cancer Institute data from 2007 to 2009, whites have about a 13 percent lifetime risk of breast cancer, blacks about 11 percent, and Hispanics less than 10 percent. The lifetime risk among Hispanics with indigenous American ancestry is even lower.

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The newly discovered SNP is on Chromosome 6, near a gene coding for an estrogen receptor known as ESR1. Fejerman and Ziv said that the biological basis of the association between the variant and reduced breast cancer risk is still not known, but their preliminary experiments indicate that the variant interferes with the action of transcription factors, proteins that regulate the expression of the ESR1 estrogen receptor.

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