Silibinin, found in milk thistle extract, is a naturally occurring flavonoid shown to have promising anticancer activity. At the University of Colorado Health Sciences Center in Denver, researchers found that silibinin was beneficial for bladder cancer. Targeting a compound called survivin, which is deregulated in bladder cancer cases, this study treated human bladder cancer cells with silibinin for 24 hours and analyzed for the presence of survivin. Treatment resulted in approximately 50% decrease in survivin, while treatments at larger doses for 24 and 48 hours showed a complete loss in survivin. The researchers also found that silibinin decreased bladder cancer cell growth.

Milk thistle extract may also be beneficial for prostate cancer. At the Georg-August-University in Germany, researchers found that silibinin was a potential agent against the spread of prostate cancer. In this study, prostate cancer cells were treated with various concentrations of silibinin in the presence or absence of DHT (dihydrotestosterone) — a substance that stimulates new cell growth). The results showed that silibinin inhibited the secretion of a biological marker of prostate cancer (PSA). Treatment with silibinin and DHT also resulted in the inhibition, while DHT alone increased PSA secretion.

The researchers concluded that the inhibition of PSA by silibinin and its counteraction on DHT mean silibinin from milk thistle may offer significant help in decreasing the risk of prostate cancer.

Sources: Biochem Biophys Res Commun. 2003 Dec 26;312(4):1178-84; J Urol. 2004 May;171(5):1934-8