FWIW, The CEGE CEO responded to a question after a recent presentation that there is no provision for stopping Vital-1 for futility since all Vital 1 patients in the experimental arm will have been treated at the time of any interim. My comment wrt the powering of Vital 1 and to its Hazard Ratio of 2 assuming a 23 month control arm median survival and a 35 month experimental arm median survival was based on a response provided by iwfal on Ihub (other than using a 22.5 median survival for the control arm) since I make no claim to being a statistician. See: http://investorshub.advfn.com/boards/read_msg.asp?message_id=24563706
It would also seem that the odds for success of Vital-1 would have increased over the three year period preceding the publication of the analysis of Taxotere TAX327 asymptomatic subgroup data since the median survival of 35 months for the high dose subgroups in the 2 Ph 2 trials (n=32) were not known until the last 8 months and the GVAX high dose smaller subgroup (n=9) that subsequently took Taxotere had still not reached median survival in September when it was already >40 months. This suggests that if crossover rates to subsequent Taxotere of the PH3 high dose patients in Vital 1 is even higher, the GVAX median survival results may be even better than Ph2. In any event, the possible treatment effect based on Ph2 GVAX high dose data has increased even more than the median survival calculated by the retrospective analysis of the TAX group asymptomatic patients over the median survival of 18.9 months previously reported for all Tax 327 patients treated with Taxotere every three weeks. The caveat, of course, is that the Provenge Ph3 increase in median survival of the integrated 9901 and 9902a patient experimental arm over their mixed control group involving crossover patients treated with the lower dose of frozen then thawed Provenge, some treated subsequently with Taxotere and some not, and some non crossover patients receiving Taxotere and some not is a far more reliable indication of 9902b results than a projection of the median survival of 32 high dose patients in Ph2 GVAX in asymptomatic AIPC to Phase 3 and a comparison to a reference Taxotere control group. If 9902b's experimental arm has the same 25.9 month median survival as that of the 9901 experimental arm and it were to be compared to a 23 month Taxotere control arm, would it be sufficiently powered to be statistically significant? Who knows? In biotech, it seems that everyone should be prepared for the unexpected. All JMHO.
Wall, the event goal and power of a survival trial is primarily driven by hazard ratio, so regardless of whether the median survival differs significantly between symptomatic and asymptomatic subpopulations, as long as the relative treatment effect as measured by hazard ratio does not differ between the these two populations greatly, then the likelihood of termination due to futility should be independent of trial population.
The question is whether the vaccine effect on risk of death can be assumed as being relatively stable. If vaccine does not perform well in the symptomatic population, then Provenge IMPACT trial would suffer, but this would mean good things for Vital-1 if it enrolls mostly asymptomatic patients. Otherwise, if vaccine does not perform well in the asymptomatic patients, then Vital-1 would suffer, however, this contradicts the prevailing thought that Provnge works better in this population which causes people to balk at the Provenge IMPACT trial.
The fact of the matter is, I think symptom unless it is of the excruciating kind that requires opioids intervention does not harm the hazard ratio. I am not alone: Gold apparently did not think Provenge treatment effect would suffer in the IMPACT trial simply due to inclusion of minimally symptomatic patients. Granted that GVAX is not exactly the same as Provenge, there is no reason to believe either of the two would be superior in terms of mechanism of action, then this belief should be able to be applied to GVAX. I haven't seen subgroup hazard ratios from the TAX327, his belief would have support if it can be shown Taxotere performs equally well in either subgroup.
I don't think Vital-1 has a higher chance of success than IMPACT, because in terms of strength of existing evidence, Provenge 9901/9902a beat GVAX phase 2 data hands down. However, the reality is that FDA and crooks collectively set back Provenge by at least a year which now gives GVAX's VITAL-1 a better positioning than before. If the halabi nomogram is to be trusted as there is no reason not to because Gold has lavishly used that to justify the IMPACT population, and that one gives due credence to the phase II GVAX observed survival of 26 months vs halabi nomogram predicted 19.6 months (which probably is within the margin of error of TAX 327's 20.3 in the asymptomatic population), then I would hypothesize that VITAL-1's interim analysis prospect would not be so bleak.
Edits: also see below from a GVAX PR as opposed to the above quoted from an ASCO 06 abstract. "Cell Genesys' ongoing Phase 3 GVAX immunotherapy for prostate cancer program is supported by the median survival results from two, independent, multi-center Phase 2 clinical trials in approximately 115 patients. The subset of patients in these two trials who received the doses comparable to the Phase 3 dose showed median survival of 34.9 months and 35.0 months, respectively. These results also exceeded the predicted survival of 22.5 months and 22.0 months, respectively, as determined by a seven point patient disease characteristic nomogram" http://www.medicalnewstoday.com/articles/76469.php
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