Soy beans, cereals and lentils contain estrogen-like compounds that counteract the effects of a common breast cancer therapy warns new research.
Of the more than 200,000 American women diagnosed with breast cancer each year, two thirds will have one of the most common forms that are fueled by the hormone estrogen.
One of the most effective therapies for these cancers use a combination of hormone therapy and an anti-estrogen drugs to combat the growth of cancer cells, doubling survival times for many women.
But a new study from Scripps University in California found that women on this combination treatment should avoid foods rich in these estrogen-mimicking compounds because they may reverse the medicine’s effects.
These compounds are not biodegradable so they are stored in our fat cells.
Two kinds of xenoestrogens had particularly adverse effects on the treatment.
The first, zearalenone, is primarily produced by the mold on corn barley, wheat and other grains.
It has been linked to birth defects and abnormal sexual development in pigs and other livestock, and is suspected of having caused an outbreak of early breast development among girls in Puerto Rico in the 1970s.
The second, a compound called genistein, is produced in certain plants including soy beans, nuts, cereals bean, lentils and rich and is often highly concentrated in food supplements.
Scientists at The Scripps Research Institute (TSRI) have discovered these two estrogen-like compounds appear to potently reverse the effects of the anti-cancer combination, palbociclib and letrozole.
Dr Gary Siuzdak, senior director of TSRI’s Scripps Centre for Metabolomics, said: ‘Breast cancer patients taking palbociclib/letrozole should consider limiting their exposure to foods that contain xenoestrogens.’
The combination hormone therapy was approved by US regulators in 2015 after a clinical trial showed it doubled the the survival time for women with these common forms of breast cancer and stopped the disease from spreading.
Letrozole blocks the production of estrogen, thus reducing the growth-promoting stimulation of ERs on breast cancer cells.
Palbociclib blocks a different signaling pathway to impede cell division and the therapy has become standard for estrogen-related breast cancers.
The study, published in Cell Chemical Biology, worked out what the individual effects of each of the two drugs were on cancer cells.
The analysis revealed that neither palbociclib alone nor letrozole alone had a strong effect on metabolites in an ER-positive breast cancer cell line.
However, the combination had a strikingly significant impact on cancer growth.
Cancer researchers are increasingly concerned that xenoestrogens in food and water may enhance the growth of estrogen-fueled cancers, and may hamper the effectiveness of anti-estrogen drugs such as letrozole.
The study examined breast cancer cells treated with palbociclib/letrozole to see how their metabolite populations changed when they were also exposed to the two common dietary xenoestrogens, zearalenone and genistein.
Even using very low doses, similar to what women might consume in food, both model xenoestrogens largely reversed the impact of the cancer drug combination including many key metabolites.
Under the influence of either compound, the breast cancer cells went back to multiplying at a rate comparable to that seen in the absence of drug treatment.
Dr Benedikt Warth at the University of Vienna, who was a visiting fellow to Prof Siuzdak’s lab said: ‘It’s intriguing that even a low, background-level exposure to these xenoestrogens was enough to impact the effect of the therapy to this degree.
‘We generally know very little about the interactions of bioactive compounds we are exposed to through our food or the environment with drug treatments.
‘So, in this field there are probably a lot of clinically relevant discoveries yet to be made.’
Results indicated these dietary compounds do have the potential to affect cancer therapy outcomes and the study looked at just two of the many estrogen-like substances commonly found in the human diet.
Dr Siuzdak added: ‘There’s a high likelihood that other xenoestrogens would counteract the therapy in a similar way.
It is not yet clear how likely it is that women’s diets would regularly include these foods, or how much of them.
‘Diet varies from person to person, and we don’t know what average levels are of xenoestrogens generally present in the blood, making it difficult to assess how different levels impact drug effectiveness,’ said Breast Cancer Now spokesperson Holly Palmer.
‘Based on current evidence, patients taking palbociclib and letrozole shouldn’t be concerned about eating foods containing these natural compounds. We’d simply encourage them to follow a healthy and balanced diet, to keep active and to try to maintain a healthy weight,’ she added.
