Minimal residual disease (MRD) is the lowest measure of detectable disease that remains present after treatment, for example 1 leukemia cell in 10,000 leucocytes. Patients responding to therapy with no detectable MRD (an MRD-negative status) generally demonstrate greater survival rates.
Minimal residual disease is vital in the development and success of various hematologic malignancy therapies; even a few rogue cells that escape treatment unscathed may grow and replicate causing a relapse. Because the test for MRD is exquisitely sensitive, physicians may use MRD measurements to assess response to current therapy or when to switch treatments. As of now, MRD measurement as a clinical diagnostic test has yet to be approved by the US Food and Drug Administration but is becoming an important endpoint in clinical trial design.
Minimal residual disease testing uses extremely sensitive techniques that can detect even a single cancerous cell among a million healthy cells. Two main methods of MRD measurements currently exist: Flow cytometry, in which particles in a fluid are detected and characterized by passing through a laser and emitting various wavelengths, and molecular sequencing, in which the fluid’s molecular composition is analyzed to reveal patterned variances. The primary hurdle in making MRD testing a diagnostic standard in treating hematologic malignancies is establishing consistent response criteria and defining an MRD-negative status.