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Old 09-12-2010, 07:18 PM   #1
Rich66
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Provenge: implications for measuring effectiveness

http://www.hemonctoday.com/article.aspx?rid=68401

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...it is not uncommon for physicians to administer drugs without having a full understanding of how they work. He said PROSTVAC-VF, a poxvirus-based vaccine composed of two recombinant vaccinia-based viral vectors containing PSA and three immune costimulatory molecules, and OGX-001, a novel anticlusterin molecule from OncoGenex, are examples of therapies that extend survival without producing any appreciable effect on time-to-progression or tumor shrinkage. “The simple explanation is that the way we measure progression in prostate cancer is problematic,” Kantoff said. “Bone scans are not terribly reliable; the majority of patients don’t have CAT-scan evident diseases. The measurements of stabilization of disease are problematic with respect to PSA.
“The other explanation is that some of these agents, most notably immunotherapies, might take a while before they work. In the Immunotherapy for Prostate Adenocarcinoma Treatment (IMPACT) trial of Provenge, the average time-to-progression is a few months. The average survival in these patients is 2 to 3 years. The effect on the immune system may occur later than an effect on progression is evident,” he said.
In the study that would be the basis for sipuleucel-T’s approval, Kantoff and colleagues recruited 512 men with metastatic castration-resistant prostate cancer and an expected survival of at least 6 months at 75 centers in the United States and Canada from August 2003 through November 2007. Researchers randomly assigned 341 patients to treatment with sipuleucel-T and 172 to placebo. Median survival was 25.8 months in the sipuleucel-T group vs. 21.7 months in the placebo group. Estimated probability of survival 36 months after randomization was 31.7% in the sipuleucel-T group compared with 23% in the placebo group.

However, sipuleucel-T did not improve median time to objective disease progression (14.6 weeks vs. 14.4 weeks) or time to clinical disease progression. Only one patient in the sipuleucel-T group had partial objective response. Eight of 311 patients (2.6%) in the experimental group who were assessed for PSA after baseline had reductions of at least 50% on two visits at least 4 weeks apart compared with two of 153 in the placebo group (1.3%).
“In patients with metastatic castration-resistant prostate cancer, the disease-progression endpoint, as currently defined, has not been a reliable predictor of overall survival,” the researchers wrote. “Several randomized trials that have shown effects of various treatments on overall survival have not shown effects on disease progression and vice versa, including one study in which a therapeutic prostate cancer vaccine was administered in a patient population similar to ours, suggesting a possible class effect or some previously unknown feature of prostate cancer.


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Old 09-13-2010, 12:33 PM   #2
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Re: Provenge: implications for measuring effectiveness

Rich,

Interesting information. Were you trying to demonstrate the lengthy process of getting a new drug approved? I found this long article about Provenge [posted in April, 2010]:

http://www.cancer.org/AboutUs/DrLens...te-Cancer.aspx
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Old 09-13-2010, 12:43 PM   #3
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Re: Provenge: implications for measuring effectiveness

Mostly pointing out how the usual tumor shrinkage/RECIST criteria gauging of effectiveness didn't predict the survival benefit. I'm wondering whether some therapies, maybe immunotherapies in particular, are abandoned prematurely due to shortsighted criteria. It also might tie into the cancer stem cell theory/issue in that they are considered a less visible but maybe important minority of the cells.
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