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ctDNA Molecular Progression — SCE Medical Oncology MCQ

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HardBreast CancerctDNA Molecular ProgressionSCE Medical Oncology

A 55-year-old woman with metastatic breast cancer on CDK4/6 inhibitor + AI has ctDNA monitoring showing a rising PIK3CA mutation allele frequency while her CT shows stable disease. What does this molecular progression predict?

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Correct answer: D — Rising ctDNA (molecular progression) typically precedes radiographic progression by 2-6 months — this may allow earlier intervention though treatment change based on ctDNA alone outside clinical trials is not yet standard practice

ctDNA dynamics (rising mutation allele frequency) can detect molecular progression weeks to months before RECIST-defined radiographic progression. This 'molecular lead time' has potential to guide earlier treatment switches, but interventional studies proving benefit from ctDNA-triggered treatment change (vs standard imaging-triggered change) in metastatic breast cancer are still ongoing (e.g. plasmaMATCH, PADA-1). Currently, ctDNA monitoring is used clinically for ESR1 mutation detection to guide endocrine therapy selection.

Reference: ESMO 2024 MBC; PADA-1 Bidard et al Lancet Oncol 2022; plasmaMATCH