ANOTHER VACCINE FAILURE FOR PROSTATE CANCER

A phase 3 clinical trial of the experimental prostate cancer therapy rilimogene (Prostvac, Bavarian Nordic) has ended because the product did not meet interim efficacy goals, the company announced last week.

The data and decision are a blow for Prostvac, which is a prostate-specific antigen-targeted vaccine designed to induce an immune system (T cell) response against the cancer.

The trial, known as PROSPECT, evaluated Prostvac as monotherapy and in combination with granulocyte macrophage colony–stimulating factor.

The study objective was to determine whether either approach, compared to placebo, could prolong overall survival in men with asymptomatic or minimally symptomatic metastatic castration–resistant prostate cancer. The study enrolled 1297 patients at more than 200 sites in 15 countries.

But the trial's independent data monitoring committee determined "that continuation [of the trial]...is futile," the company said in a press statement.

The experimental therapy has gained some buzz in the prostate cancer treatment community, in part owing to results from a small, early-stage trial presented in 2015 that showed notable efficacy in combination with the immunotherapy ipilimumab (Yervoy, Bristol-Myers Squibb). The vaccine is also being studied in combination with nivolumab (Opdivo, Bristol-Myers Squibb).

The vaccine's manufacturer, Bavarian Nordic, hopes that the cancer vaccine can complement these drugs.

"While this is certainly not the desired outcome, we remain steadfast believers in the power of combination treatments, including immunotherapies, to transform the future of cancer therapies," Bavarian Nordic CEO Paul Chaplin, PhD, said in last week's statement.

Prostvac employs two poxviruses (vaccinia and fowlpox) in its vaccine regimen. Currently, there are 19 ongoing or completed clinical studies with more than 2000 patients; most of those patients have been treated with Prostvac, according to the company.

Prostvac is being developed in collaboration with the National Cancer Institute under a cooperative research and development agreement. Bavarian Nordic has also partnered with Bristol-Myers Squibb to commercialize the product.

Follow Medscape senior journalist Nick Mulcahy on Twitter: @MulcahyNick

For more from Medscape Oncology, follow us on Twitter: @MedscapeOnc