In a Phase I clinical trial, which outcome is primarily evaluated to determine safety?

• A. Cure rate improvements
• B. Overall survival
• C. Dose-limiting toxicities
• D. Regulatory approval

Answer: (C)

In early-stage trials, safety is determined by looking for dose-limiting toxicities. A DLT is a predefined, treatment-related adverse event of sufficient severity that occurs within a specified early period and prevents increasing the drug dose. Observing DLTs at a given dose helps establish whether that dose is tolerable and guides the determination of the maximum tolerated dose for future studies. Other outcomes like cure rate or overall survival are later, larger efficacy endpoints evaluated in subsequent phases, and regulatory approval comes after full safety and efficacy data are reviewed. So the key safety signal in Phase I is the occurrence and pattern of dose-limiting toxicities.