‘Strong research’ shows plant-based compounds can reduce breast cancer recurrence
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Key takeaways:
- Green tea consumption associated with a reduction in risk for breast cancer recurrence.
- Additional research needed to know if consumption before diagnosis or after treatment makes a difference in outcomes.
Certain natural compounds derived from soy and other plants can significantly reduce the risk for breast cancer recurrence or death, data published in JNCI Cancer Spectrum suggest.
The analysis revealed an association between consumption of soy isoflavones and reduced risk for breast cancer recurrence, as well as an inverse association between serum or plasma enterolactone levels and mortality, according to researchers.
Data derived from van Die MD, et al. JCNI Cancer Spectr. 2024;doi:10.1093/jncics/pkad104
“It is critically important to stress that these studies were conducted on women who received medical and/or surgical treatment for breast cancer, and that these foods and phytonutrients should not be considered as alternatives to treatment,” Channing Paller, MD, director of prostate cancer clinical research and associate professor of oncology at Johns Hopkins Medicine, said in a press release. “This research highlights the need for more robust studies in this area looking at the most effective dosages of these compounds, and whether starting to consume them after diagnosis has the same effect as a lifelong dietary habit before diagnosis.”
Background and methodology
Intake of phytonutrients may improve outcomes following a breast cancer diagnosis for some individuals, according to background information provided by study investigators. However, little is known about the impact of postdiagnosis introduction compared with established prediagnosis exposure of these nutrients, as well as their optimal dosage.
Researchers conducted a systematic review and meta-analysis to evaluate the impact of phytonutrient consumption on survival outcomes in women with breast cancer.
They searched MEDLINE, Embase, CINAHL, Cochrane Library, ClinicalTrials.gov and ISRCTN registry for both prospective and retrospective observational studies evaluating the potential impact of soybean, lignans, cruciferous vegetables, green tea or their phytonutrients.
The final meta-analysis included data from 32 studies.
Results, next steps
Researchers reported 26% reduced risk of breast cancer recurrence associated with exposure to soy isoflavones (HR = 0.74; 95% CI, 0.6-0.92), most notably among postmenopausal survivors (HR = 0.72; 95% CI, 0.55-0.94) and estrogen receptor-positive survivors (HR = 0.82; 95% CI, 0.7-0.97).
Researchers observed the greatest risk reduction at a dosage of 60 mg/day.
Regarding mortality outcomes, reduction in risk for death typically occurred within the 20-40 mg/day range.
Study investigators noted an inverse association between soy protein/products and cancer-specific mortality for estrogen receptor-positive disease (HR = 0.75; 95% CI, 0.6-0.92), with an inverse association observed between serum or plasma enterolactone — measured prediagnosis and early postdiagnosis — and both cancer-specific mortality (HR = 0.72; 95% CI, 0.58-0.9) and all-cause mortality (HR = 0.69; 95% CI, 0.57-0.83).
Further analysis showed a 44% risk reduction for breast cancer recurrence with prediagnostic green tea for women with stage I and stage II breast cancer (HR = 0.56; 95% CI, 0.38-0.83); no effects were noted for cruciferous vegetables.
Additional research is needed to fully understand the relationships observed across the various studies, according to study investigators. Nevertheless, they added, the results suggest certain measurable benefits associated with consumption of the nutrients included in the analysis.
“These findings were graded probable, which means there is strong research that they contributed to the results we are seeing,” Diana van Die, PhD, a member of National Institute of Complementary Medicine Health Research Institute at Western Sydney University, said in a press release.
References:
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The apparent benefit of soy was most pronounced among women who had hormone-sensitive breast cancer. Interestingly, moderate soy intake — about one to three servings per day — was associated with the greatest benefits, with no advantage to greater amounts of soy consumption.
The findings also suggested that green tea consumption of three or more cups daily prior to breast cancer diagnosis was associated with more favorable breast cancer outcomes. The study was not able to demonstrate significant associations between breast cancer outcomes and intake of cruciferous vegetable and lignans — found in whole grains, beans, seeds, certain fruits and vegetables — but serum of plasma levels of enterolactone, a metabolite of lignans, did appear to correlate with improved breast cancer-specific survival and OS among postmenopausal women.
Limitations to observational studies addressing diet and nutrient intake include reliance on patient reporting and recall of diet, as well as an inability to control for other factors that may be associated with certain dietary patterns. Additional limitations in this meta-analysis include the small number of studies addressing some of the phytonutrients under study and differences in timing of exposure assessment, with some addressing nutrient intake prior to diagnosis and others evaluating patients after diagnosis.
This study does not tell us whether changes in phytonutrient intake after breast cancer diagnosis will affect breast cancer outcomes. It does, however, add to the growing literature supporting the safety of moderate soy and phytoestrogen intake for those with or at risk for breast cancer.
It should be noted that one’s overall diet — including fiber, types of fats, protein and total caloric intake — are likely to impact health more than any one individual class of nutrient.
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