Not quite all quiet on the prostate front

There has been almost no new prostate cancer news over the past few days, which accounts for the general lack of new posts to this page and (probably) for the overblown reporting of the potential utility of a modified form of measles virus in treatment of prostate cancer.

According to a report in Science Daily on Friday: “A new study … has found that certain measles virus vaccine strain derivatives … may prove to be an effective treatment for patients with advanced prostate cancer. The findings show that this type of treatment, called virotherapy, can effectively infect, replicate in and kill prostate cancer cells.”

We wish to emphasize the complete truth of this statement. However, it is somewhat less than the whole truth (at least in so far as we can ascertain).

The actual paper by Msaouel et al., originally published in The Prostate last November, reported on studies with the measles virus derivative MV-CEA. The abstract of that paper did not make or imply the sorts of claims that are now appearing in the media! It suggested that in preclinical (laboratory studies) and in animal studies using special laboratory mice with induced prostate cancer tumors, this virus derivative clearly has biological activity — which is great.

Media reports, as exemplified by the article in Science Daily, go somewhat further:

“The median survival time of MV-CEA-treated mice in the study almost doubled compared to the controls, and complete tumor regression was observed in one-fifth of treated animals.

“‘Based on our preclinical results as well as the safety of measles derivatives in clinical trials against other tumor types, these viral strains could represent excellent candidates for clinical testing against advanced prostate cancer, including androgen resistant tumors,’ says Evanthia Galanis, M.D., of the Mayo Clinic, senior author of the study.”

So what we really appear to know is that MV-CEA was capable of inducing a complete response (which is by no means the same as complete elimination of cancer) in the treatment of 20 percent of a special type of mouse that has been given a special type of prostate cancer in the laboratory compared to a placebo (in the “control” mice). This is a less than revolutionary biological effect.

It gets worse. If the virus can actually be used in humans (which is not yet known), it would have to be injected into the actual prostate cancer tumor tissue. And the Science Daily article states with enthusiasm that: “Because primary tumor sites are easily accessible in prostate cancer, locally recurrent disease represents a promising target for virotherapy approaches. The virotherapy agent can easily be applied directly to the prostate tumor via ultrasound-guided needle injections and close monitoring of therapy can be achieved by non-invasive techniques including ultrasound and MRI.”

This statement is filled with problematic implications. Let me just list a few:

  • Determining whether a patient with a rising PSA after first-line treatment really has only locally recurrent disease is near to impossible. One may be able to treat the locally recurrent disease one can identify, but that doesn’t mean you’ve treated the micrometastases you can’t see.
  • The accuracy with which techniques like MRI and ultrasound can be used to identify small foci of locally recurrent disease is significantly less than 100 percent. Therefore, you couldn’t possibly be sure you had found and treated all foci of locally recurrent disease.
  • Even if MV-CEA works as well in humans as it works in carefully managed laboratory mice, it would still only have an good shot at effectiveness in one in five patients (at best).

The scientific potential of genetically modified viruses to treat cancer is still only in the very early stages of investigation. The great promise of such viruses is that they are likely to be extremely safe — if they can be made to be effective. However, it is still going to be many years before such a virus derivative is shown to have significant clinical impact in the treatment of prostate cancer in man based on currently available science. This does not, of course, preclude the type of scientific breakthrough that changes the clinical opportunities, but we don’t see such a breakthrough in this study.

2 Responses

  1. Wow! Thank you!

    I always wanted to write in my blog something like that. Can I take part of your post to my blog?

    Of course, I will add backlink?

    Regards, Reader

  2. Dear “Reader”: Please go right ahead (so long as you add the promised backlink).

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