Measurable residual disease (previously known as “minimal residual disease”) refers to the small number of cancer cells that remain in the body after successfully completing anti-cancer treatment. Although unlikely, these cells have the potential to cause disease relapse.
To track and measure these cells in patients, oncology providers use measurable residual disease (MRD) testing. These tests can detect very small quantities of remaining malignant cells in a person that previous methods may have missed. While typical assays can detect malignant cells down to a level of approximately 1 in 100, MRD assays can detect cancerous cells down to 1 in 100,000 or even 1 in 1 million using next-generation sequencing or next-generation flow cytometry.
In oncology practice, MRD testing can be used to:
Though these tests are mainly used for blood cancers (e.g., leukemia, lymphoma, and multiple myeloma), its applicability to additional cancers is currently being studied.
MRD Testing in Chronic Lymphocytic Leukemia
Chronic lymphocytic leukemia is a type of cancer of the blood and bone marrow. The term "chronic" indicates that this type of leukemia typically progresses more slowly than others, and MRD for this disease refers to the number of leukemic cells that can be detected in peripheral blood or bone marrow after a patient completes treatment.
As new treatments like immunotherapies become more effective treating patients with chronic lymphocytic leukemia, patients’ MRD testing will often reveal no or only minimal residual disease in their peripheral blood or bone marrow specimens. These negligible amounts of cancer have shown to be indicative of longer progression-free survival and, in some cases, overall survival.
These developments have led to an emerging need for sensitive methods to quantify residual disease in patients after chemotherapy or bone marrow surgery. And there is growing interest in using MRD testing as a more effective prognostic biomarker for chronic lymphocytic leukemia and other cancers.
MRD Testing in Multiple Myeloma
The efficacy of new multiple myeloma treatments is demonstrated through the large numbers of patients who are now achieving complete remission and extended periods free of progression. Given that multiple myeloma is an incurable disease with relapses that can eventually lead to death, being able to accurately determine the exact amount of MRD in a patient’s body after treatment is essential.
Knowing the amount of residual disease in a patient can help guide treatment decisions and predict the likelihood of relapse. Due to this testing’s effectiveness, MRD is now the most reliable marker of treatment response and subsequent prognostication of patients with multiple myeloma.
Testing for measurable residual disease can shape treatment choices and patient management to achieve better outcomes. Unfortunately, routine MRD testing among patients varies considerably, despite updated recommendations demonstrating the prognostic significance of this testing. Insurance coverage also varies; it is difficult for under-insured and uninsured patients to access this pricey testing.
To help expand the use of MRD testing, it is essential for members of the multidisciplinary cancer care team—from oncologists to nurses and social workers—to better understand the purpose, use, and significance of this testing in all cancer treatment settings, including community-based practices.
MRD testing has the potential to become a reliable marker of treatment response for patients with multiple myeloma and chronic lymphocytic leukemia upon full integration into clinical practice. ACCC’s CANCER BUZZ podcast features two guests who discuss the benefits of MRD testing for these specific patient populations, the importance of training multidisciplinary care teams, and the promise of MRD testing to improve patient outcomes as its adoption continues to grow.
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