The genistein saga — all data and no (good) results

The idea that the soy isoflavone known as genistein might prove to be a non-toxic therapeutic agent for the prevention and/or treatment of prostate cancer has now been around for so long that the idea appears to have become a perceived truth in some quarters. Unfortunately that perception of truth is still not supported by any well-documented clinical effects in men that actually have or are at significant risk for prostate cancer, even though a PubMed search for “genistein” and “prostate cancer” promptly brings up links to nearly 400 published articles going back to the early 1990s.

Despite the lack of any significant clinical effects to date, a report from the news center at Northwestern University yesterday  managed to make the claim that “researchers at the Robert H. Lurie Comprehensive Cancer Center of Northwestern University have found that a new, non-toxic drug made from a chemical in soy could prevent the movement of cancer cells from the prostate to the rest of the body.” Even in the kindest of dreams, describing genistein as a “new, non-toxic drug” requires a vivid imagination!

According to the report, some new “findings” about genistein are to be presented at the upcoming American Association for Cancer Research Frontiers in Cancer Prevention Research Conference. The new findings appear to come from a small study of patients with localized prostate cancer who were treated with genistein either before and after radical prostatectomy or only after their surgery. According to the study protocol (which was initiated back in 2002), the expected trial enrollment was 88 patients. The trial report mentions only 38 patients.

The results of this study seem to be limited to some (poorly characterized) biological effects noted in cancer cells extracted from the prostates of patients post-surgery:

  • Patients treated with genistein before surgery demonstrated
    • Increased expression of “genes that suppress the invasion of cancer cells”
    • Decreased expression of “genes that enhance invasion” of cancer cells

Quite what that means would be difficult for any clinician to interpret. We aren’t even sure yet exactly which genes are truly important to the progression of prostate cancer! We have to assume that the changes in gene expression reported are as compared to the levels in patients who only received the genistein after surgery.

On the basis of the results of this study, the research team now wants to start another phase II study (in 36 patients) to see if [genistein] can stop the cancer cells from moving out of the prostate and into the rest of the body.” They suggest that if this is the case, genistein could become “the first therapy for any cancer that is non-toxic and targets and inhibits cancer cell movement.”

The problem with all of this is that:

  • It would probably be impossible to get a patent on genistein as a drug for the treatment of cancer today.
  • If there ever was a patent, it has surely run out by now.
  • If one can’t get a patent, who is going to pay for the trials to prove all of this?

The real issue, of course, is that genistein probably doesn’t have sufficiently significant clinical impact. A study by deVere White et al., published in Urology back in 2004, and based on a cohort of 62 patients, reported that “A genistein-rich extract as the sole treatment for [prostate cancer] did not reduce PSA levels by 50 percent or more in 51 of 52 subjects. Thus, it does not appear to be an effective treatment for [prostate cancer] when given alone.” deVere White and his colleagues did point out however, that 8/13  patients in the active surveillance group in this study had either no rise or a decline of < 50 percent in their PSA levels. Might it be worth studying the value of genistein therapy in men on active surveillance? Perhaps.

But guess what! de Vere White and his colleagues have done that study too! Published this month in Nutrition and Cancer, their report indicates that they carried out a double-blind, randomized, placebo-controlled trial in 53 men with prostate cancer already enrolled in their active surveillance program. The treatment group was given a supplement containing genistein (450 mg), daidzein (300 mg), and other isoflavones daily for 6 months. Their results show that giving patients these high levels of isoflavones can lead to significantly elevated serum concentrations of genistein and daidzein, but there was no sign whatsoever that isoflavone therapy reduced the  PSA levels in men with low-volume prostate cancer.

We suspect it’s well past time to bury genistein — at least as a possible treatment for prostate cancer.

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