MAR 06, 2017 07:39 PM PST

Timing is Everything in the Cancer-Soy Connection

WRITTEN BY: Carmen Leitch

Scientists at Georgetown Lombardi Comprehensive Cancer Center have investigated the relationship between soy consumption and breast cancer in animal models, finding a mixed bag of effects. In rodents, the researchers revealed the mechanism by which soy intake reduces the recurrence of breast cancer and boosts the efficacy of a breast cancer drug tamoxifen. However, the work also indicates why consuming soy-based foods for the first time during tamoxifen treatment can actually have a negative impact, the reduce effectiveness of tamoxifen, and promoting cancer recurrence. The results, summarized in the video below from Time Magazine, have been reported in the journal Clinical Cancer Research; they show why consumption especially of the most active isoflavone in soy, genistein, influences tamoxifen.

The senior investigator of the work, Leena Hilakivi-Clarke, PhD, a Professor of Oncology at Georgetown Lombardi, indicated that their findings reflect the experience of breast cancer patients.  "There has long been a paradox concerning genistein, which has the similar structure as estrogen and activates both human estrogen receptors to a degree. Estrogen drives most breast cancer growth, yet high soy intake among women in Asian countries has been linked to a breast cancer rate that is five times lower than Western women, who eat much less soy," explained Hilakivi-Clarke. "So why is soy, which mimics estrogen, protective in Asian women?"

Breast cancer that is considered positive for estrogen receptors impacts over 70 percent of those diagnosed, 1.67 million women globally in 2012. Endocrine treatments are supposed to lessen estrogen's ability to encourage cancer growth, and are the most typical treatment. While some endocrine breast cancer therapeutics are effective, about half of those treated are not responsive or the cancer comes back. 

The scientists employed a more advanced breast cancer and tamoxifen model in their rats to implicate the timing of genistein intake as the critical factor. Lead researcher Xiyuan Zhang explained that sustained intake of genistein over a long time prior to the development of breast cancer improves the overall resistance to cancer, which acts as a shield against the development and recurrence of cancer.

"It also inhibits a mechanism called autophagy that would allow cancer cells to survive, which explains why it helps tamoxifen work," says Zhang, who was a member of Hilakivi-Clarke's laboratory at the time of this work, and is now a postdoctoral researcher at the National Institutes of Health.

Previous studies that were done in women have not found an adverse effect from soy intake on breast cancer outcome, said the researchers, who added that research also indicates that intake of as little as 1/3rd cup of soymilk daily or 10 mg. of isoflavones, in Asian and Caucasian women resulted in the lowest rate of breast cancer recurrence. However, the data from animal studies show that starting to eat or drink soy after the development of breast cancer may not be a good idea.

Initiating genistein intake following breast cancer development in animals did not start an immune response against the tumor, Zhang said. "We do not know yet why this made the animals resistant to the beneficial effects of tamoxifen and increased risk of cancer recurrence," she continued.

Animals exposed to genistein as adults  had a 7 percent chance of breast cancer recurrence following treatment with tamoxifen treatment, while a 33 percent recurrence was seen in rats consuming genistein only after the start of breast cancer development.

"We have solved the puzzle of genistein and breast cancer in our rat model, which perfectly explains the paradox seen in earlier animal studies and patients," saidHilakivi-Clarke. "While many oncologists advise their patients not to take isoflavone supplements or consume soy foods, our findings suggest a more nuanced message -- if these results hold true for women. Our results suggest that breast cancer patients should continue consuming soy foods after diagnosis, but not to start them if they have not consumed genistein previously."

Sources: ScienceDaily via Georgetown University, Clinical Cancer Research

About the Author
  • Experienced research scientist and technical expert with authorships on 28 peer-reviewed publications, traveler to over 60 countries, published photographer and internationally-exhibited painter, volunteer trained in disaster-response, CPR and DV counseling.
You May Also Like
JUL 18, 2018
Immunology
JUL 18, 2018
Immunotherapy Increases Survival of Melanoma Brain Metastases Patients
Use of Checkpoint Blockade Immunotherapy increases survival rates in Melanoma Brain Metastases patients, with a 4-year survival rate increase from 11.1% to 28.1%...
JUL 30, 2018
Cancer
JUL 30, 2018
Challenges Coming to a Cancer Diagnosis in the UK
England's NHS Cancer Patient Experience Survey shows some cancers take longer for GPs to recognize....
OCT 04, 2018
Genetics & Genomics
OCT 04, 2018
Similar Processes Drive the Development of Lung and Prostate Cancers
Small cell cancers often have poor prognoses....
OCT 06, 2018
Genetics & Genomics
OCT 06, 2018
Genetic Mutation Linked to Increased Pancreatic Cancer Risk in Women
In a first, researchers have found a genetic mutation that has a sex-specific effect on pancreatic cancer risk....
NOV 06, 2018
Genetics & Genomics
NOV 06, 2018
New Gene is Implicated in a Rare Cancer
Rodents are known as common research models, but zebrafish have been gaining ground as an attractive alternative for many reasons....
NOV 24, 2018
Drug Discovery
NOV 24, 2018
New Anti-Malarial Drug Target in Cancer
For decades, anti-malaria drugs--known as Chloroquines, have used to treat cancer. But the role in repurposing these drugs for slowing tumor growth have ne...
Loading Comments...