Risks from selenium — in men WITH prostate cancer

A recent study from researchers at the University of California, San Francisco and the Dana-Farber Cancer Center is now suggesting that elevated selenium levels in the blood may worsen prostate cancer outcomes in some men who already have the disease.

Frankly, The “New” Prostate Cancer InfoLink is not overly surprised by this possibility. We already knew from the SELECT trial that selenium has no beneficial impact in the prevention of prostate cancer (either on its own or in association with vitamin E) , and there were some signals in that trial that selenium was associated with specific adverse events in some men.

The recent report by Chan et al. in the Journal of Clinical Oncology indicates that prostate cancer patients with high as compared to low serum selenium levels are associated with a 35 percent increase in likelihood of presenting with aggressive disease. And for men who carry specific genes for a particular enzyme known as manganese superoxide dismutase  (SOD2), the implications may be very important.

Many prior studies have appeared to suggest that selenium might have an effect in reducing the risk of prostate cancer.  But the SELECT trial appears to have disproved that hypothesis. Based on their own earlier work, Chan and her colleagues hypothesized that SOD2  might affect the association between selenium level and risk of aggressive prostate cancer at time of diagnosis.

They therefore evaluated the presence of three genetic variants of SOD2 (AA, VA, and VV) — based on the two different A and V “alleles” for SOD2 — as well as the levels of plasma selenium in 489 patients diagnosed with localized or locally advanced prostate cancer who were all part of another study.

They were able to show that:

  • SOD2 genotype alone was not associated with disease aggressiveness.
  • Higher versus lower selenium levels were associated with a slightly increased likelihood of presenting with aggressive disease (relative risk or RR = 1.35).
  • The SOD2 variant appeared to be related to the impact of selenium levels on prostate cancer aggressiveness, as follows:
    • Among men carrying only the A allele (i.e., men with the AA variant), higher selenium levels were associated with a reduced risk of presenting with aggressive disease (RR = 0.60).
    • Among men carrying the V allele (i.e., men with the VV or the VA variant), higher selenium levels were associated with an increased risk of aggressive disease (RR = 1.82)

The authors conclude that circulating selenium levels in the blood may be affected by SOD2 genotype and that this suggests caution against broad use of selenium supplementation for men with prostate cancer.

Quoted in a related media release about this study issued by the Dana-Farber Cancer Center, Dr. Phillip Kantoff, the senior author of this study, states that, “If you already have prostate cancer, it may be a bad thing to take selenium.” He goes on to comment that, “These findings are interesting particularly in light of the recent negative results from the SELECT prevention study, which asked if selenium could protect against prostate cancer.”

The results of the current study only go to emphasize the fact that one cannot make simplistic assumptions about how to manage illness based on apparent “associations” that are unsupported by real clinical evidence. Despite the years of media stories that “antioxidants can help people live longer, healthier lives with a lowered risk of cancer,” it isn’t appropriate to immediately make the assumption that antioxidants will be beneficial if one is diagnosed with a specific form of cancer. To quote Dr. Kantoff again, once you have cancer, “then antioxidants may be a bad thing.”

Dr. Phillip Kantoff is a member of the Scientific Advisory Board of The “New” Prostate Cancer InfoLink.

5 Responses

  1. So I take Prostate 2.3 Vitamin, as instructed by my doctor, after being diagnosed and having prostate removed. They changed the formula to decrease the vitamin E and selenium in their 2.3 version. But based on these reports should I stop taking?

    Current ingredients: 100 IU vitamin E (as mixed tocopherols); 2,400 IU vitamin D3 (as cholecalciferol); 70 mcg selenium (as selenomethionine)
    30 mg lycopene (as Lyc-O-Mato®); 50 mg soy isoflavones (as Novasoy®)

  2. Dear Mike:

    You would need to discuss that with your doctor. We cannot make specific clinical recommendations for specific patients since we are not physicians and do not have all of the relevant data.

  3. Hi, Sitemaster or Dr. Kantoff:

    Question re availability of SOD2 genotype testing …

    Having fast-rising PSA, to 9.4, but got negative 12-needle
    biopsy a week ago, confirmed by a second-opinion pathology
    report. Was taking selenium. Where can I
    get a serum test for A versus V allele? I could call it my
    own “research” project, not that you’d want to endorse
    research this way. I am responsible for my own decisions,
    and for my own judgments concerning the validity and
    usefulness of data. I would like to see if stopping the
    selenium slows my PSA velocity. I may have to get
    a re-biopsy done with the color-flow Doppler ultrasound.
    My urologist assured me the grayscale was just as good.

  4. Dear Mr. Andrews:

    I am sorry but I have no idea whether such a test is commercially available at all.

  5. Thank you for your reply, and thanks to all of you involved with this important work. May you all reap rich material and spiritual rewards for your virtues.

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