Measurable residual disease (MRD) testing provides a sensitive measure of treatment response in multiple myeloma (MM) and can help refine risk assessment, guide monitoring, and inform long-term prognosis.

MRD is a very important tool in the treatment of MM. The questions are: How do we define it, and why is it important? To me, MRD is the best available lens for determining how deep the response really is in patients with MM. It moves beyond the partial and complete responses that we have used for years. The reason it matters is simple: deeper responses tend to translate into longer remissions. And, in practice, MRD helps us have more honest conversations with patients about their prognosis. In select situations, it can also inform how intensively we follow patients with MM over time.

In terms of timing, I think that MRD is most useful at clinical decision points, such as after major treatment phases and when the patient has achieved what appears to be the best response. The goal is not to do the test repeatedly just because we can, but rather to measure the depth of response when it can meaningfully refine risk assessment and our expectations for treatment.

Most MRD testing currently relies on highly sensitive bone marrow–based assays. However, MM can be patchy, and bone marrow sampling is only one window into the disease. So, the key point is that MRD is powerful but not perfect—which is why interpretation is important. The results should be interpreted in context, ideally complemented by imaging and the full clinical picture. In routine practice today, the practical uses of MRD are for risk refinement and effective communication. MRD helps us distinguish good responders from exceptional deep responders, and it can help determine how closely we monitor patients. I am cautious about using MRD as a single trigger to escalate or stop therapy outside of a structured approach; it is not a stand-alone decision.

As we know, MRD negativity is a great sign, but it is not a guarantee of cure because the disease may simply be below the limits of detection at that time. MM biology can still declare itself later, so I frame MRD negativity as a marker of excellent disease control, not a promise of cure. The higher the biologic risk, the more I view MRD as a monitoring and prognostic tool rather than a reason to deintensify treatment. It may give you more flexibility in a standard-risk patient with sustained deep response. In high-risk disease, however, even deeper response does not erase the underlying biology of the disease. It tells you that you are winning, but you still need a long-term plan.

The future of MRD is making it more comprehensive and more actionable. “Comprehensive” means integrating bone marrow testing with imaging and blood-based approaches. “Actionable” means embedding MRD-guided decisions into clear evidence-based pathways. The endgame is not MRD on its own, but rather a smarter individualized therapy. The US Food and Drug Administration (FDA) correctly adopted MRD negativity as a surrogate marker for approving a drug for MM. Patients may be waiting a long time for a drug to be FDA approved based on progression-free or overall survival. Overall, I think that incorporating MRD negativity as a marker for effective drugs is a great success and service to patients with MM while confirmatory studies are pending.