skip to main content

5-FU Expected Reaction — SCE Dermatology MCQ

Instant feedback + full explanation. One question, done properly.

EasySkin Cancer5-FU Expected ReactionSCE Dermatology

A 55-year-old man with multiple actinic keratoses on his scalp has had field treatment with topical 5-fluorouracil 5% cream. During treatment he develops marked erythema, crusting, and erosions in the treated area. Is this expected?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: B — Yes — the inflammatory reaction is the expected pharmacological response indicating the 5-FU is destroying dysplastic keratinocytes; it is a marker of treatment efficacy

The inflammatory reaction during topical 5-FU treatment for AKs is the desired pharmacological response — 5-FU selectively damages rapidly dividing dysplastic keratinocytes (which take up the antimetabolite preferentially), causing erythema, crusting, erosion, and pain. The intensity of the reaction correlates with the density of subclinical AKs in the treated field. Patients must be counselled BEFORE treatment about this expected reaction (which can be dramatic) and that it indicates the treatment is working. The inflammation resolves 2-4 weeks after completing the course, leaving treated skin smoother with fewer AKs. If the reaction is too severe, the application frequency can be reduced (e.g., alternate days) or interrupted briefly.

Reference: BAD 2017 AK; BNF