Investors in the USA could barely hide their enthusiasm as Cell Genesys reported promising data from a second mid-stage trial of its new treatment for prostate cancer.

The company’s shares leapt 30% at the close of trading on the Nasdaq to $5.70 as it unveiled results from a second multi-centre Phase II trial of its GVAX immunotherapy which evaluated escalating doses of the treatment in 80 patients with metastatic hormone-refractory prostate cancer (HRPC).

Cell Genesys said that additional follow-up of the 22 patients who received the dose that is comparable to that being employed in an ongoing Phase III programme indicates that the median survival is 35 months, compared with a predicted survival of 22 months. The company had previously reported results from its first Phase II trial of GVAX immunotherapy in 34 patients which showed an overall median survival of 26.2 months and data from both studies compare favourably to the previously-published median survival of 18.9 months for HRPC patients treated with Sanofi-Aventis’ Taxotere (docetaxel) chemotherapy plus prednisone, the current standard of care.

GVAX immunotherapy is comprised of two prostate cancer cell lines that have been modified to secrete GM-CSF (granulocyte-macrophage colony stimulating factor), an immune stimulatory hormone, which plays a key role in kick-starting the body's immune response. Cell Genesys noted that GVAX immunotherapy is currently being studied as a single agent and in combination with docetaxel chemotherapy in two Phase III trials expected to enroll approximately 1,200 patients with metastatic HRPC and the company has received ‘special protocol assessments’ from the US Food and Drug Administration for each of the studies. It has also received ‘fast-track’ designation for the product.

What is also of interest to analysts is the fact that Cell Genesys’ product is being developed as a non patient-specific, "off-the-shelf" pharmaceutical, unlike Dendreon Corp's therapeutic prostate cancer vaccine Provenge (sipuleucel-T), which last week received a positive recommendation from an FDA regulatory panel. The latter is patient-specific, ie it uses a patient's own tumour cells to generate a vaccine intended to stimulate a strong immune response against malignant cells, and analysts claim that the latter involves highly complex manufacturing issues.

Observers believe that Dendreon’s Provenge still has a long way to go to get full FDA approval but its panel’s positive recommendation has got investors excited about the potential for cancer immunotherapies and Cell Genesys is at the head of the pack.