**4.12 Minimal residual disease**

In every NDMM patient, there are an average of 3 to 5 clones present. These clones undergo mutations at varying degrees throughout the treatment course, with progression of disease presenting expansion of resistant clones over time. As a result, multiple myeloma is not considered to be a curable disease, and so an evolving treatment aim has been for maximal disease burden reduction [71]. The ability to reduce disease burden beneath the threshold of detection, known as minimal residual disease (MRD), has been shown to be an important prognostic indicator for survival and long-term outcomes. MRD has traditionally been detected by flow cytometry (sensitive to 104 cells) and next generation sequencing (NGS) (sensitive 106 cells). An evolving consensus is that achieving MRD-negative status at the time of induction therapy should be the goal of therapy. Though not-yet involved in staging systems, MRD-focused treatment assessments are becoming increasingly important with time [72].
