What Is Minimal Residual Disease?
Minimal residual disease (MRD) is a condition that refers to the small number of cancer cells that stay in the body after cancer treatment. The number of cells remaining may be very low in number that they may not cause any signs or symptoms. These cells may be so small that they cannot be detected by using traditional diagnostic methods like taking a blood smear and viewing it under the microscope or investigating serum proteins in the blood. Patients with positive test results for MRD means there are still residual (remaining) cells in the body, and the disease or cancer is still there, and vice-versa in case of negative MRD test results.
What Is the Role of Minimal Residual Disease Assessment in Patient Care?
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Minimal residual disease (MRD) means residual of a small number of cancer-causing cells that is in the person during treatment, or after treatment. The presence of minimal residual disease in blood cancers has been a significant diagnostic method to measure the response of optimal drug therapy at the extensive level of detection of MRD in the body. The absence of MRD in bone marrow or negative result after completion of induction drug therapy appears to provide a good prognosis.
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However, if there is still disease detected after the treatment, it is referred to as MRD positive as the cancer cells are still in the body. Therefore, the treatment can be extended or changed to get rid of these extra cancer cells and to get the results as MRD negative.
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In another case of MRD-positive patients, the testing of minimal residual disease can be done many times to monitor the progression of the disease more extensively.
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Minimal residual testing is one of the prime factors that may help in reducing the risk of relapse and can provide essential information on chromosome abnormalities, type of disease, and blast cell count.
What Is the Need for Minimal Residual Disease Testing?
Minimal residual testing has several important functions, such as-
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It helps in determining whether the treatment has eliminated the cancers like leukemia (cancer of the body's blood-forming tissues), myeloma (cancer of plasma cells), or whether there are some traces (residual cells) still present in the body.
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Comparing the effectiveness of different treatments for cancer.
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Monitoring the patient emission status and detecting the recurrence rate of conditions like leukemia or melanoma.
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Choosing the most appropriate treatment.
When Would Doctors Test for MRD?
The healthcare professionals will advise minimal residual disease testing based on varying factors specific to the disease. Patients may be tested for MRD in the following cases which include:
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After bone marrow transplantation.
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During cancer treatment.
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After the completion of the last cycle of planned combination therapy (more than one method of treatment).
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After one year of maintenance therapy (treatment that is done to prevent cancer from coming back after it has been eradicated following the initial treatment).
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To confirm the severity of remission.
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This can also be done at regular intervals after the treatment is completed.
What Techniques Are Used to Detect Minimal Residual Disease?
There are multiple tests used for the detection of minimal residual disease and are very highly sensitive tests. In these tests, a sample of bone marrow cells is taken by aspiration with the help of a needle or from peripheral blood cells that are taken through the vein. The diagnostic tests done in this condition include:
1. Flow Cytometry - This technique helps to evaluate the cells of a person by detecting certain protein markers on the cell surface. For this test, a fresh bone marrow sample is taken for reliable results. This bone marrow aspirate sample is treated with special antibiotics that get attached to the cells that have a specific protein on their surface. Depending upon the method, this test may help in detecting one cancer cell among 100,000 bone marrow cells, and the results may be available within one day.
2. Polymerase Chain Reaction (PCR) - This is one of the most commonly used methods. In this technique, the specific trace amount of DNA (Deoxyribonucleic acid) is evaluated by expanding the DNA segment. By this technique, the malignant (cancerous) cells can be identified based on their characteristic genetic abnormalities, which may include mutations or chromosomal changes. The polymerase chain reaction technique works by increasing or amplifying a small number of distinctive pieces of DNA (Deoxyribonucleic acid) or RNA (Ribonucleic acid) so that it is easier to count or detect any abnormality. Moreover, genetic abnormalities can even be detected by PCR in cases with a very small number of cancer cells remaining in the body. With this method, it is possible to detect one cancer cell within 100,000 to one million normal cells. The only disadvantage of this method is that it may take several weeks to get the results.
3. Next-Generation Sequencing (NGS) - This method may include several different sequencing technologies. In this technique, the multiple numbers of DNA or RNA stretches can be examined simultaneously. This test may help in detecting various mutations and other genetic abnormalities in DNA extracted from the bone marrow sample. This is a highly sensitive test and can detect one cancer cell in one million bone marrow cells. The test results are usually available within a week.
What Do the Results Mean?
The test results are usually available as negative MRD or positive MRD. The negative MRD result means that there is no cancer. This means that there is no more cancer left in the body, and the treatment has been effective. According to various studies, it has been found that this test result provides better outcomes and longer remissions for different types of cancers like multiple melanomas or other blood cancers.
On the other hand, a positive MRD test result means that the cancer cells are still present in the body. This means that there is still a risk of having cancer, and this may also indicate that there is a need to formulate a new treatment plan.
What Treatment Options Are Available for Minimal Residual Disease?
The treatment depends upon the test results of MRD. A negative test result means there is no need for further treatment, and a positive test result means there is a need for treatment or change the previous treatment and looking for more options, which may include -
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Stem Cell Transplant - In this, the damaged bone marrow cells are replaced with healthy ones.
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Targeted Therapy - In this method, specific drugs or other substances are used to target specific molecules responsible for causing cancer.
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Combination Therapy - This includes using a combination of different treatments, which may include chemotherapy, radiation, and other treatments.
However, the treatment method may depend upon the following options which may include -
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Previous treatment.
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The type of blood cancer.
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The overall health of the patient.
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The number of residual cancer cells in the body.
Conclusion
The minimal residual disease is a criterion used to detect the progression of cancer treatment and to verify whether it has been eradicated from the body or not. This acts as a marker which may also help in choosing the best treatment for the patient to prevent the reoccurrence of cancer. Therefore, MRD acts as an important diagnostic tool for providing information that ultimately will help in providing the best treatment for the best potential prognosis.
