Shares in Cell Genesys have collapsed after the US firm said it has called a halt to a late-stage trial of its investigational prostate cancer immunotherapy GVAX due to a higher-than-expected number of patient deaths.

The California-based company has terminated the second of two Phase III trials of GVAX on the recommendation of the study's independent data monitoring committee after it "observed an imbalance in deaths between the two treatment arms." The study included 408 patients with hormone-refractory advanced prostate cancer who were randomised to receive either GVAX in combination with Sanofi-Aventis' Taxotere (docetaxel) or Taxotere plus prednisone.

However, the IDMC recommended ending the trial after it identified 67 deaths among patients receiving GVAX and Taxotere, compared with 47 deaths in the control arm. Cell Genesys said that at this time "a specific cause for the imbalance in deaths has not been identified” and the IDMC reported no new safety issues for GVAX when administered in combination with the Sanofi drug.

Cell Genesys chief executive Stephen Sherwin expressed his disappointment and said that “the observation in the VITAL-2 trial is very surprising to us”. He added that the firm has also asked the IDMC to conduct “a previously unplanned futility analysis” of VITAL-1, a separate Phase III trial involving 626 patients with earlier stage disease, “in order to determine the overall prospects for our ongoing development programme for this product”. The results of that analysis will be known in a month’s time, though the IDMC said in January that VITAL-1 should continue.

Dr Sherwin added that with the termination of VITAL-2, “we expect to make commensurate adjustments to our business operations” and further details of this will be made public “in the near future”. He noted that the company ended the second quarter of 2008 with $166 million in cash.

Investors were equally disappointed and the stock hit an all-time low to close down 72% at $0.79. However analysts at Canaccord Adams believe the picture is not as gloomy as the share price suggests.
Joseph Pantginis issued a note saying that earlier clinical trials, and the ongoing VITAL-1 tests demonstrate that the vaccine “has clearly been effective and prolonged survival”. However, “the perception will be, for a while, because one of these studies failed, the other one will fail", he added.

Nevertheless, “if the data seen in Phase II hold up in the VITAL-1 study, it's a clearly approvable drug in our opinion," Mr Pantginis added.