New VaccinePromising for Patients with Metastatic Prostate Cancer
By Laszlo Dosa
ORLANDO—A phase 3 trial is underway of a cancer vaccine (Gvax), a vaccine currently under investigation for several types of cancer, including patients with hormone-refractory metastatic prostate cancer. This allogeneic whole-cell tumor vaccine was developed from 2 prostate cancer cell lines, rather than taken directly from patients, which have been genetically modified to secrete granulocyte-macrophage colony-stimulating factor, a hormone that plays a key role in activating the body’s immune response to vaccines.
atalie Sacks, MD, of the University of California San Francisco and director of clinical research at Cell Genesys, the manufacturer of the vaccine,reported at the 2005 Multidisciplinary Prostate Cancer Symposium that the phase 2 trials were promising. “One trial showed that a group of hormone-refractory prostate cancer patients had a median survival of 26 months at the single-arm phase 2 trial…much longer than we expected, compared with the natural history of the disease.”
The phase 3 trial is enrolling approximately 600 patients who are free of cancer-related pain and will compare the vaccine to docetaxol (Taxotere),a chemotherapy agent. One half of the randomized patients will receive the vaccine every 2 weeks for up to 6 months, while the remaining patients will receive chemotherapy. The patients will be followed for the remainder of their lives. According to Dr Sacks, the trial is designed to demonstrate at least a 33% improvement in the duration of survival, which is the primary end point of the study.
A second trial comparing the vaccine plus chemotherapy with chemotherapy alone is currently being planned.
Michael Carducci, MD, of Johns Hopkins University, Baltimore, Md, said that based on the encouraging results so far, the dose response and immunologic activity warrant the large phase 3 studies that are planned. “The safety profile, the fact that you can see PSA responses, and the immunologic effect, suggest that they have to sort of hang in there before they get the overall survival benefits. Gvax might be one of the opportunities for patients at this point,” he told IMWR.