Recently, there has been some minor controversy regarding the use of milk thistle extract in women with a history of breast cancer. For example, the Susan Komen for the Cure website ( states: “Theoretically, because milk thistle plant extract might have estrogenic effects, women with hormone-sensitive conditions should avoid milk thistle above-ground parts . . .. The more commonly used milk thistle seed extracts are not known to have estrogenic effects.”

The Problem With Fuzzy Logic

Is there any validity to these concerns? Not really. What is sad is that such cautions may keep women who really could benefit from taking a milk thistle extract from doing so. Most milk thistle extracts are made from the seed, so these cautions popping up on many websites as well as in newsletters are really irrelevant. On the flip side, the research is quite promising on using milk thistle extract as both a preventive substance as well as a possible therapeutic aid in breast cancer patients. Some of the beneficial effects noted in the many scientific investigations of milk thistle extracts containing silymarin and its major constituent, silibinin, include:

  • Prevention of the expression of genes and enzymes pivotal in breast cancer development
  • Inhibition of breast cancer cell growth and the key pathways that cancer cells use to grow
  • Promotion of apoptosis (programmed cell death) in breast cancer cells

New Data

Unregulated protein synthesis is a key event in the development of breast cancer. Regulation of protein synthesis is required for cell growth, proliferation, differentiation and cellular homeostasis. Loss of this regulation leads to excessive growth in cancer cells—the greater the loss, the more aggressive the cancer. The primary regulator is messenger RNA (mRNA) which in turn is influenced by translation initiation factors that lead to the expression of the code on the mRNA. Silibinin has been shown to block the signaling of these translation initiation factors in a new and very novel manner, via a very specific molecular mechanism that can inhibit growth of cells that have been transformed into cancerous cells.


Lin CJ, Sukarieh R, Pelletier J. Silibinin inhibits translation initiation: implications for anticancer therapy. Mol Cancer Ther. 2009 Jun;8(6):1606-12

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