The reason for the excitement is recent data (presented at the American Urological Association annual meeting) showing a modest improvement in prostate cancer survival rates - a 4.1 month increase, with a 3-year survival rate of 42% compared to 23% for the control group. Oddly, the drug extends survival without shrinking tumours. However, Forbes reports that there is some concern over study design:
Much of the skepticism about Provenge until now has related to the perceived limitations of the 500-person study that Kantoff helped run. It was too small, some experts thought, and had an unusual design in which patients who did not receive Provenge and saw their cancer get worse would receive a frozen-then-thawed version of the vaccine.What's cool, though, is that if it works and is approved it will be the first cancer vaccine. The treatment itself is manufactured in part from a person's own antigen presenting cells (APCs, in this case dendritic cells). Patient APCs are extracted and co-cultured with a recombinant fusion protein. The now antigen-loaded APCs are then reinfused where they potentially activate a T-cell response against prostate cancer cells. The full course consists of 3 treatments over 4 weeks with only mild side effects compared to standard chemo treatments.
This is unusual and may be unprecedented, says Donald Berry, head of biostatistics at the M.D. Anderson Cancer Center. It is possible that this frozen-then-thawed vaccine is actually different from Provenge; if it somehow harmed patients (there's no proof it does), it would actually make Provenge appear more effective. He asks how patients did after their cancer had progressed.
While the survival increase is quite small, it's encouraging and at least highlights the possibility of this kind of therapy. It would be interesting to know the duration of the immune response. Could this method be used as a preventative measure? How effective would it be against other cancers? (using a different antigen, of course)