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Flax Oil and Herceptin

Jacob Schor ND, FABNO

July 13, 2010


Flaxseed oil enhances effect of Herceptin against HER2+ breast cancer:

In recent years the number of published medical studies that lend support to our therapeutic recommendations has increased greatly, not just in quantity, but in size, and quality as well.  No longer are we relying on small in vitro studies or animal studies.  The monthly Naturopathic Doctors News and Review that I contribute articles to now strongly dissuades my referencing any animal studies; they only want references to human trials.  The Natural Medicine Journal, another regular outlet for my contributions, asks me to consider writing only about human clinical trials that are less than 12 months old. Typically, I am able to pick studies to write about that are less than two months old. As the scientific literature on which we rely on for evidence that what we do works, grows in quantity and quality, we have begun to get fussy.

Yet, I've printed out a paper this morning that describes a mouse study that I feel compelled to write about because the information, if it holds true in human trials, is so clinically relevant that it seems silly to wait until those human studies are published.

This paper, which came out May 21, 2010 in the journal Food and Chemical Toxicology and was written by Julie Mason and her colleagues at the University of Toronto, examined the effects of flax seed oil on select breast cancer cells and how it reacted with a specific chemotherapy drug Trastuzumab.

Flax seed oil is often taken by patients believing that it has an anti-cancer effect.  I confess to not having promoted its use in the past as the evidence has been relatively weak to support use.  Far better evidence supports the use of flax seed meal.  The meal contains a much higher level of lectins than the oil and these chemicals have been considered responsible for benefits when it comes to breast cancer.  Nevertheless, use of flax oil remains high, promoted by many websites that have not let lack of evidence curtail their prescriptions.

Mason and her colleagues looked at how flax seed oil interacts with the drug Trastuzumab (TRAS).  This drug, commonly called Herceptin, is the primary drug now used to treat epidermal growth factor receptor 2 (HER2) positive breast cancer.  When breast cancer pathology reports come back telling us that a tumor is HER2 +, this is not considered good news.  Thus anything that may help in treating this particular subgroup of women is of interest, even if the research was only done in mice.

In this study HER2+ human breast cancer cells were implanted in immune deficient mice.  The mice were experimentally given flax seed oil as part of their diet and various doses of Trastuzumab. In the Control Group of mice who received neither oil or drug, the tumors grew unchecked, increasing in size by 187% over the four weeks the experiment lasted.

Trastusumab was given at two different doses.  The tumors in the mice receiving the lower dose (2.5 mg/kg body weight) did not grow, staying the same size through the course of the study, confirming that this is a decent treatment option for women with HER2+ breast cancer.

The higher dose of TRAS (5mg/kg body weight) worked better than the low dose; the tumors significantly ‘regressed,’ that is got smaller by 75%.  This appears to be a case where more is better. 

The mice who received flax seed oil did even better.  The tumors in those mice who got the low doses of the drug and also given flax seed oil, regressed by 89%.  In the high drug dose plus oil mice the tumors regressed 84%.  Curiously more drug was not necessarily better.

Tumor sizes were tracked for several weeks after the drugs were stopped and the results got even more interesting.  The benefit seen in the low dose drug plus flax seed oil mice continued even after stopping the drug so that two weeks after the drug was stopped the tumors in the low drug dose plus oil mice were still 87% smaller than in the mice that only received the drug at low doses. The tumors tied in size with the mice that had been given the drug in high doses.  

The concerns often expressed by medical oncologists that the supplements prescribed by naturopathic doctors seem, in this particular situation, to be unfounded.  This study's abstract reaching the conclusion: “Flax seed oil did not interfere with Trastuzumab but rather enhanced its tumor-reducing effects and combined flax seed oil and low dose Trastuzumab was as effective as high dose Trastuzumab treatment.”

The doses used in this study were about equivalent to the doses used in women with breast cancer.

“Initial dose of 4mg/kg as an intravenous infusion over 90 minutes then at 2 mg/kg as an intravenous infusion over 30 minutes weekly during chemotherapy for the first 12 weeks (paclitaxel or docetaxel) or 18 weeks (docetaxel/carboplatin).”

Translating dosing information obtained from mice to humans is never an easy task but if the data obtained in this study were to hold true in humans, adding flax seed oil to a patient’s regimen might enhance the effect of the chemo during the 12 weeks of 2 mg/kg dosing.

The dose of flax seed oil used in these mice is equivalent to 1-2 Tablespoons per day for a person.

There is no question that we would prefer to see the results of a human trial than of a mouse experiment before accepting this information as fact.  Still, once one ponders the potential benefit that might be obtained, it is very hard to ethically argue in favor of waiting until such data is published.


Food Chem Toxicol. 2010 May 21. [Epub ahead of print]

Flaxseed oil-trastuzumab interaction in breast cancer.

Mason JK, Chen J, Thompson LU.

Department of Nutritional Sciences, Faculty of Medicine, University of Toronto, 150 College Street, Toronto, ON M5S 3E2, Canada.


Flaxseed oil (FO), which is rich in n-3 fatty acid, is commonly consumed by breast cancer patients because of its potential anti-cancer effects. Trastuzumab (TRAS) is the primary drug for epidermal growth factor receptor 2 (HER2) positive breast cancer. We investigated in athymic mice whether combining dietary FO (8%) with TRAS treatment (2.5 or 5mg/kg body weight) can cause better or adverse effect on established human breast tumors overexpressing HER2 (BT-474). Control tumors significantly grew 187%, TRAS2.5 treated tumors did not change, while TRAS5, FO+TRAS2.5 and FO+TRAS5 treated tumors significantly regressed 75%, 89% and 84%, respectively, after 4 weeks treatment. Two weeks after stopping TRAS treatment while continuing on same diet, tumor size in FO+TRAS2.5 group was 87% lower than in TRAS2.5 group and was not different from TRAS5 group with or without FO. Combined TRAS2.5 treatment with FO caused a significantly lower tumor cell proliferation and higher apoptosis compared to TRAS2.5 treatment alone and showed similar effect to TRAS5 treatment with or without FO. Hence, FO did not interfere with TRAS but rather enhanced its tumor-reducing effects and combined FO and low dose TRAS was as effective as high dose TRAS treatment. Copyright © 2010. Published by Elsevier Ltd.