UCLA researchers have discovered that for women with a relatively common inherited genetic mutation, known as the KRAS-variant, an abrupt lowering of estrogen in the body may increase the risk for breast cancer and impact the biology of their breast cancer. Scientists also found that women with the KRAS-variant are more likely to develop a second primary breast cancer, independent of a first breast cancer.

The two-year study, led by Dr. Joanne Weidhaas, a professor of radiation oncology at the UCLA Jonsson Comprehensive Cancer Center and director of translational research at the David Geffen School of Medicine, analyzed data from more than 1,700 women with breast cancer who submitted DNA samples to be tested for the inherited KRAS-variant. The study also included a group of women with the KRAS-variant who were cancer-free, as well as biological models to scientifically confirm the clinical findings.

Weidhaas’ team found that acute estrogen withdrawal, as experienced after removal of the ovaries or when hormone replacement therapy was discontinued, and/or a low estrogen state were associated with breast cancer in women with the KRAS-variant. Acute estrogen withdrawal also triggered breast cancer formation in KRAS-variant biological models used in the study. In addition, up to 45 percent of breast cancer patients with the KRAS-variant eventually developed a second independent breast cancer — representing a 12-fold greater risk than women with breast cancer who did not have the KRAS-variant.

“Although we had evidence that the KRAS-variant was a stronger predictor of cancer risk for women than men, we did not previously have a scientific explanation for this observation,” Weidhaas said. “This study’s findings, showing that estrogen withdrawal can influence cancer risk for women with the KRAS-variant, begins to provide some answers.”

The findings are contrary to some past research suggesting that women on combination hormone replacement therapy are more likely to develop breast cancer, but the study is in agreement with follow-up studies which found that estrogen alone might actually protect women from breast cancer.

“The KRAS-variant may be a genetic difference that could actually help identify women who could benefit from continuing estrogen, or at a minimum, at least tapering it appropriately,” Weidhaas said. “We hope that there are real opportunities to personalize risk-reducing strategies for these women, through further defining the most protective estrogen management approaches, as well as by understanding the impact of different treatment alternatives at the time of a woman’s first breast cancer diagnosis.”

The study was published in the journal Cell Cycle.

The research, which was supported by the National Cancer Institute, was done in collaboration with MiraKind, a nonprofit organization.