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Health News Archive 341 - Lung Cancer
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Milk Thistle Protects Against Lung Cancer

A flavanone compound in milk thistle, silibinin, stopped lung cancer growth and spread in mice, says research from the University of Colorado.

Lung cancer is the most common form of cancer worldwide with over 1,200,000 new cases diagnosed annually, according to the European School of Oncology. It has one of the lowest survival rates with only 25 per cent of patients surviving more than one year after diagnosis.

The new research, published in the Journal of the National Cancer Institute did not use milk thistle dietary supplements, but pure silibinin, the active component in milk thistle.  “Milk thistle extract dietary supplements generally contain 80 per cent silymarin, a flavonolignan mixture; and silymarin contains approximately 40 per cent silibinin,” explained Singh.  “Therefore, we expect about 32 per cent (w/w) silibinin in milk thistle dietary supplements,” he said.

The researchers divided 90 mice into six groups of 15 mice each and injected 75 mice with cancer-causing urethane (cancer development in two to three weeks) and 15 mice with a saline solution (control).  After two weeks of eating a normal diet, the urethane-treated mice were fed a diet supplemented with different doses of silibinin (zero, 0.033, 0.10, 0.33, 1.0 per cent).

After 18 weeks, the silibinin supplemented group had between 32 and 38 per cent less tumors than the urethane-only group, across all the dose range. After 29-weeks, the silibinin supplemented group had between 64 and 70 per cent less tumors than the urethane-only group, across all the dose range.  Mice that received the 1.0 per cent silibinin supplement had 93 per cent fewer large tumors than the urethane-only group.

In terms of cancer spread, the tumors in the silibinin supplemented mice had between 41 and 74 per cent fewer cells that tested positive for proliferation (spread) markers.  The formation of blood vessels (angiogenesis) was also found to be reduced in the silibinin groups, with reductions up to 89 per cent recorded.

“Our most clinically relevant observation was that silibinin prevented tumors from growing beyond a small size in a dose-depended fashion,” said the researchers.  “We believe that this inhibition is due, at least in part, to the inhibitory effect of silibinin on angiogenesis.”  The mechanism behind the effects is not clear, but the researchers suggest that the flavanone may act on the expression of two enzymes (iNOS and COX-2), as well as the vascular endothelial growth factor (VEGF), which promote tumour angiogenesis. 

The authors caution that the animal model of lung cancer, while similar, does not mirror human lung cancer. A comparable dose in a 150 pound human would be in the range of about 2 to 20 grams per day for the three lower doses, said Singh.  While this may sound like a lot, Singh said that research has indicated such doses of silibinin are not toxic.

“A recent study in human prostate cancer patients suggest that silibinin consumption up to about 6.7 g/day does not show any significant adverse health effect.  “This study is still continuing with escalated doses of silibinin to find out the maximal tolerated dose in the patients,” said Singh. Milk thistle (Silybum marianum) has been used for a long time as a food in Europe. Young leaves are used in salads, the stalks eaten like asparagus, and the heads boiled like artichoke.

Source: Singh, R. P., G. Deep, et al. (2006). "Effect of silibinin on the growth and progression of primary lung tumors in mice." J Natl Cancer Inst 98(12): 846-55.

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