Schering-Plough ended its partnership with Novacea after its prostate cancer compound Asentar failed in clinical trials. The companies ended a late-stage study of the drug late last year citing an "imbalance" of deaths. Patients taking Asentar died more often than those taking a standard treatment. Asentar rights will be returned to Novacea. Despite the higher-than-expected number of deaths, the company said in published reports it still believes Asentar is a safe drug and called Schering-Plough's decision unexpected.