Minimal Residual Disease — Trace Cancer Cells

Minimal residual disease, often abbreviated to MRD, describes a state where an extremely low level of malignant cells persists following anti-cancer therapy. These cells are undetectable using conventional diagnostic methods, such as routine microscopic examination of blood or bone marrow, or standard radiological imaging like CT scans.

Advanced laboratory technologies, including flow cytometry and molecular genetic assays, are required to detect these remaining cells. Achieving an MRD-negative status means that sensitive testing found no residual malignant cells within the limits of the test, representing a deep therapeutic response.

MRD status provides critical information about the depth of your remission and your risk of recurrence. Rather than waiting for symptoms or visible tumours to reappear, doctors use MRD testing as an early indicator of treatment response. An MRD-negative result generally indicates a lower likelihood of relapse and may allow some individuals to avoid unnecessary further treatments. Conversely, persistent or rising MRD levels can alert clinicians to consider additional interventions, such as maintenance therapy or stem cell transplantation, before a clinical relapse occurs.

MRD is assessed using highly sensitive techniques performed on bone marrow aspirates or peripheral blood samples. Multiparameter flow cytometry identifies malignant cells by their unique surface protein patterns. Molecular tests, including quantitative polymerase chain reaction and next-generation sequencing, detect cancer-specific genetic mutations or rearranged immunoglobulin genes, often finding one cancer cell among a million healthy cells.

MRD testing is most commonly utilised in haematological malignancies. It is a standard component of management in acute lymphoblastic leukaemia, acute myeloid leukaemia, chronic lymphocytic leukaemia, and multiple myeloma. Researchers are also actively investigating the concept of molecular residual disease in solid tumours, such as colorectal, breast, and lung cancers, using circulating tumour DNA in the bloodstream.

MRD results directly guide treatment decisions. If MRD is detected, doctors may recommend continuing consolidation chemotherapy, introducing targeted therapies, or planning an allogeneic stem cell transplant. In certain leukaemias, specific immunotherapies are licensed exclusively to eradicate MRD. Conversely, sustained MRD negativity may allow safe treatment de-escalation in clinical trial settings.