They monitor safety in all three clinical trial phases and beyond. Note for example the outcome measures for the Provenge PIII:
Primary Outcome Measures: To assess the safety and efficacy of Sipuleucel-T in prolonging survival of men with Metastatic Androgen Independent Prostate Cancer [ Time Frame: Overall Survival (time to death) ] [ Designated as safety issue: Yes ]
Secondary Outcome Measures: To assess the safety and efficacy of Sipuleucel-T in delaying time to objective disease progression in men with Metastatic Androgen Independent Prostate Cancer [ Time Frame: Time to objective disease progression ] [ Designated as safety issue: Yes ]