Provenge finally meets expectations

Dendreon's pivotal Phase III IMPACT (IMmunotherapy for Prostate AdenoCarcinoma Treatment; also known as D9902B) study of Provenge (sipuleucel-T) in men with advanced prostate cancer (PCA) has met its primary endpoint of improving overall survival (OS) compared to placebo. The magnitude of the survival difference observed in the intent-to-treat population resulted in the study successfully achieving the prespecified level of statistical significance defined by its design. The safety profile of Provenge appeared to be consistent with prior studies.

The 512-patient, randomised, placebo-controlled study enrolled men with metastatic androgen-independent PCA and was conducted under a Special Protocol Assessment (SPA) agreement with the FDA. Because the data meet the criteria and specifications outlined in the SPA, Dendreon intends to file an amendment to its existing BLA in the fourth quarter of this year. News of the success triggered a huge jump in the company's share price. After closing on 13th April at US$7.30, the stock rose to a high of US$22.10 on 14th April, a 202 per cent increase.

It is expected that Dendreon will form an international partnership in the third quarter of the year to commercialise the vaccine, although the company will likely market Provenge alone in the US. Some analysts predict that once approved, Provenge could reach peak annual sales of US$2 billion. The vaccine is expected to achieve rapid uptake based on the survival benefit and good safety profile alone.

Detailed results from the trial will be presented during a plenary session at the American Urological Association Annual Meeting, to be held from 25th to 30th April, in Chicago, IL. Provenge may represent the first in a new class of active cellular immunotherapies specifically designed to engage the patient's own immune system against cancer.

Although the success of the trial has been heralded as a breakthrough for therapeutic cancer vaccines, it has also reignited debate about the FDA’s strict guidelines for drug approvals, and especially for innovative medicines. Two years age, the Agency decided not to approve Provenge despite an endorsement by one of its Advisory Committees, which recommended that there was substantial evidence supporting the efficacy and safety of the vaccine. In making its recommendations, the Advisory Committee was asked if the submitted data established that Provenge was reasonably safe and whether there was substantial evidence that the product was efficacious. The Advisory Committee voted 17 to 0 in favour of the safety of Provenge and 13 to 4 in favour of the efficacy question.

However, the FDA went against the Advisory Committee and requested additional clinical data in support of the efficacy claim contained in the submission. Now that the results are available from the IMPACT study, the FDA will be under increasing pressure to approve the vaccine, especially as the conditions in the SPA that the Agency agreed with Dendreon look to have been met. What could now stand in the way of approval? Possibly, quality control regarding the manufacture of the vaccine.

Matthew Dennis - Editor, Cancer Drug News