Minimal residual disease: premises before promises

Minimal residual disease (MRD), a measure of residual cancer cells, is a concept increasingly employed in precision oncology, touted as a key predictive biomarker to guide treatment decisions. This paper critically analyzes the expanding role of MRD as a predictive biomarker in hematologic cancers. I outline the argument for MRD as a predictive biomarker, articulating its premises and the empirical conditions that must hold for them to be true. I show how these conditions, while met in paradigmatic cases of MRD use in cancer, may not hold across other cancers where MRD is currently being applied, weakening the argument that MRD serves as an effective predictive biomarker across cancer medicine.