Patient with pigmentation (diffuse dark melanotic streaks) on buccal mucosa, tongue, and cheeks — patient under radiotherapy/chemotherapy. Diagnosis:

Correct answer: A. Chemotherapy-induced melanocyte stimulation

• A. Correct. Certain chemotherapeutic agents can stimulate melanocyte activity, producing diffuse mucosal hyperpigmentation, consistent with this patient's history of recent chemo/radiotherapy.
• B. Physiologic pigmentation is a longstanding, typically symmetric finding present since a young age, not a new finding correlating with recent chemotherapy.
• C. Addison's disease pigmentation is due to elevated ACTH, an endocrine cause unrelated to this patient's chemotherapy history.
• D. Amalgam tattoo is a localized, not diffuse, pigmented lesion from embedded amalgam particles, and unrelated to chemotherapy.