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Photodynamic Therapy — SCE Dermatology MCQ

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HardDermatological SurgeryPhotodynamic TherapySCE Dermatology

A 55-year-old man with extensive superficial BCC on his trunk is being treated with PDT. His nurse applies methyl aminolaevulinate (MAL) cream under occlusion for 3 hours, then illuminates with red light at 630 nm. He experiences significant pain during illumination. What is the mechanism of tumour destruction in PDT?

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Correct answer: C — MAL is converted to protoporphyrin IX in tumour cells, which generates reactive oxygen species on illumination, causing oxidative cell death

The best answer is “MAL is converted to protoporphyrin IX in tumour cells, which generates reactive oxygen species on illumination, causing oxidative cell death”. BAD guidance stratifies BCC by site, subtype, border and margin status; high-risk or incompletely excised disease requires specialist discussion, while treatment should balance clearance, function and tissue preservation. The alternatives “Chemical dissolution of tumour cells by the cream, within an appropriate UK pathway, after clinicopathological correlation, after specialist assessment”, “Mechanical disruption from the dressing, after clinicopathological correlation, after specialist assessment, when the full phenotype supports it, within an appropriate UK pathway”, “UV-induced DNA damage, after specialist assessment, when the full phenotype supports it, within an appropriate UK pathway, after clinicopathological correlation”, “Direct thermal burn from the light source, when the full phenotype supports it, within an appropriate UK pathway” are clinically adjacent possibilities, but they do not fit the defining morphology, distribution, histopathology, risk signal or management sequence in this stem.

Reference: BAD basal cell carcinoma guideline 2021: https://academic.oup.com/bjd/article/185/5/899/6599942