Which of the following best describes the role of promoters in chemical carcinogenesis?
- A They cause direct DNA mutations that initiate carcinogenesis
- B They act at the promotion stage by forming DNA adducts
- C They stimulate clonal expansion of initiated cells without being mutagenic themselves ✓
- D They are complete carcinogens that can cause cancer independently
Correct answer: C. They stimulate clonal expansion of initiated cells without being mutagenic themselves
Explanation
Promoters stimulate the proliferation of initiated (mutated) cells and allow clonal expansion, but are not themselves mutagenic and do not cause cancer independently — they require prior initiation. Classic examples include phorbol esters (TPA/PMA), which activate protein kinase C and drive cell proliferation. Initiators cause irreversible DNA mutations; complete carcinogens can both initiate and promote. Promoters do not form DNA adducts.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
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