Which statement best describes a cell cycle–specific chemotherapeutic agent?

• A. DNA replication
• B. Preparation for mitosis
• C. Agents that target specific phases of the cell growth cycle
• D. Tumorcidal agents whose action is not dependent on the cell cycle

Answer: (C)

Cell cycle–specific agents are drugs that exert their cytotoxic effects only during particular phases of the cell growth cycle. They are most effective when cancer cells are actively progressing through those targeted phases, such as DNA synthesis in the S phase or mitosis in the M phase. Because their action depends on the cell being in a specific phase, they’re best described as agents that target specific phases of the cell growth cycle. The other statements don’t define this concept: focusing on a single process like DNA replication is too narrow, and naming only preparation for mitosis misses the broader idea of phase-specific targeting. And describing agents whose action is not dependent on the cell cycle refers to cell cycle–nonspecific agents, which is the opposite of what’s being described.