A cancer drug does not appear in one step. It moves through a chain of stages, and each stage answers a different question.
Discovery begins with a biological idea: some molecule in or on a cancer cell seems to matter for the disease. Researchers then search for a chemical compound that can act on it. Before anything is given to a person, the compound is tested in laboratory systems and in animals for basic safety and signs of activity.
Only then does it enter human testing. Early trials ask mainly whether the drug is safe and how the body handles it. Later trials ask whether it actually helps patients compared with existing care. If the evidence holds up, regulators review the full body of data, and only after approval does the drug reach routine clinical use.
The important feature of this chain is that it is sequential and cumulative. Time spent at one stage is not recovered later, and a failure at any stage sends the program back to an earlier question — or ends it. The cost of the whole journey is dominated by the stages that involve human testing, because those stages are the slowest and the most resource-intensive.