Which statement correctly describes the relationship between tumor cell growth rate and chemotherapy?

• A. Faster growing cells are less susceptible to chemotherapy
• B. Non-dividing cells are more susceptible to chemotherapy
• C. Faster growing cells are more susceptible to chemotherapy
• D. Slower growing cells are more susceptible to chemotherapy

Answer: (C)

Chemotherapy tends to be most effective when tumor cells are actively dividing. Many cytotoxic drugs disrupt DNA replication or mitosis, processes that are more common in cells that are rapidly proliferating. Therefore, tumors with a high growth fraction have more cells in vulnerable stages of the cell cycle (like S or M phase) and are more susceptible to these agents than slow-growing tumors, whose cells spend more time in non-dividing states. Non-dividing cells are relatively resistant because the drugs have fewer active targets. This principle also explains why chemotherapy often causes side effects in other rapidly turning-over tissues, such as bone marrow and the lining of the gut. While drug type and tumor biology can modify this relationship, the general rule is that faster-growing tumors are more responsive to chemotherapy.