Minimal residual disease

Minimal residual disease (MRD) is the name given to small numbers of leukaemic cells (cancer cells from the bone marrow) that remain in the patient during treatment, or after treatment when the patient is in remission (no symptoms or signs of disease). It is the major cause of relapse in cancer and leukemia. Up until a decade ago, none of the tests used to assess or detect cancer were sensitive enough to detect MRD. Now, however, very sensitive molecular biology tests are available, based on DNA, RNA or proteins. These can measure minute levels of cancer cells in tissue samples, sometimes as low as one cancer cell in a million normal cells.