ASCO: Flaxseed May Slow Prostate Cancer Growth

CHICAGO, June 3 -- Flaxseed supplementation significantly reduced cancer cell proliferation rates in men with prostate cancer, investigators in a multicenter study found.

Flaxseed, alone or combined with a low-fat diet, slowed cell growth rates compared with diet alone or a control group, said Wendy Demark-Wahnefried, Ph.D., of Duke University.

However, she told attendees at the American Society of Clinical Oncology, other biomarkers of prostate cancer activity were unaffected by the supplement.

Flaxseed is one of the richest known sources of lignans, which affect androgen metabolism and have antimitotic, antiangiogenic, antioxidant, and estrogenic effects, said Dr. Demark-Wahnefried.

Flaxseed also is the richest known source of plant-derived omega-3 fatty acids, which influence cell membrane synthesis, circulating levels of protein kinase C and tyrosine kinases, and levels of natural killer cells, she said.

Studies have also suggested that a low-fat diet inhibits prostate cancer cell growth, she added.

To continue the evaluation of flaxseed, Dr. Demark-Wahnefried and colleagues randomized 161 patients scheduled for radical prostatectomy to four groups: flaxseed supplementation only, a low-fat diet (?20% of calories from fat) only, flaxseed supplementation plus a low-fat diet, or a control group that had neither intervention.

Adherence to the active interventions was good, said Dr. Demark-Wahnefried; patients followed the requirements of the randomized groups almost 7 days a week.

All of the men in the study were at least 3 weeks away from their scheduled surgery. Cellular proliferation and apoptosis rate were assessed in malignant and benign prostate tissue at enrollment and before surgery. The primary endpoint was median tumor proliferation rate at end of treatment.

Median proliferation rate (MIB-1 volume) was 1.5 in patients randomized to flaxseed and low-fat diet, 1.66 in the flaxseed-only group, 2.56 in the low fat-diet group, and 3.23 in the control group (P=0.0013). The proliferation rate did not differ between patients randomized to flaxseed alone or in combination with a low-fat diet.

Adverse effects were similar and occurred at similar rates across the four treatment groups.

"Further study is needed to validate these findings using the presurgical model, and to determine the effects using other models, such as after biochemical failure," said Dr. Demark-Wahnefried.

"It is also necessary to disentangle potential synergies between the low-fat diet and flaxseed supplementation and to determine whether the effects are related to lignan or to fat." Finally, she concluded, "it is necessary to determine potential mechanisms underlying these effects."

Studies such as the one reported by Dr. Demark-Wahnefried provide physicians with information to respond to some of the most common questions that patients pose in clinical practice, commented Bruce Cheson, M.D., of Georgetown University. Patients want to know whether the vitamins, herbs, and other nonprescription products they hear about and frequently use actually do any good.

"Most of the time we don't know, frequently because the studies haven't been done yet," said Dr. Cheson. "We take our cancer advances wherever we can get them. Many of our new chemotherapy drugs are actually derived from natural products: taxanes, vincristine, all-transretinoic acid, just to name a few."