The drugmaker disclosed that patients with advanced prostate cancer who received its experimental med - ZD4054 - lived around seven months longer than those on placebo, according to results of a clinical trial. But the drug failed to show an improvement in progression-free survival, a measure of how long patients survive before their condition worsens, Reuters reports.

Two months ago, AstraZeneca claimed the drug demonstrated overall survival benefits and was being moved into final Phase III studies. The results are extremely important to the drugmaker, which hopes the new med will revive its fortunes, although filing for approval wouldn’t happen until 2009.

A salve for prostate cancer is a hot topic this year, mostly due to the controversy over Dendreon’s Provenge vaccine and an FDA decision to delay approval. Normally, men with advanced stage disease are given hormonal therapies, which can be highly effective. But as Reuters notes, resistance often develops, leaving Sanofi-Aventis’s Taxotere chemo drug, which improves survival by around 2.4 months, as the only option.

Nick James, professor of clinical oncology at the Institute for Cancer Studies in Birmingham, England, says the Phase II trial results with the new once-daily pill were “promising.” In the study of 312 pain-free or mildly symptomatic patients, the median survival time for those on 10 milligrams of ZD4054 was 24.5 months, compared with 17.3 months for placebo. Those given a 15 mg dose of the drug lived 23.5 months. But the study failed to show a statistically significant difference in progression-free survival (PFS), which had been its primary endpoint.

“It is usual to use PFS as an endpoint in Phase II studies, however it can be difficult to measure accurately in patients with metastatic HRPC. Overall survival is an unambiguous endpoint and clearly an important outcome for patients,” James tells Reuters.

Industry analysts said ZD4054 could be a blockbuster, with potential annual sales above $1 billion, if it proved successful in final Phase III and regulators were convinced of its benefits, Reuters writes. The field is littered with prostate cancer drugs that have not won approval, including a similar product called Xinlay from Abbott Labs, which was rejected by the FDA two years ago after failing to delay disease progression.

ZD4054 works by blocking the action of a cell protein called endothelin A, which is believed to play a key role in prostate tumour growth.