Minimal Residual Disease (MRD), also called measurable residual disease, refers to a small number of cancer cells that may remain in the body during or after treatment. These cells can be difficult to identify through conventional diagnostic methods because their quantity may be extremely low. MRD testing uses specialized laboratory technologies to detect these remaining cancer cells or their biological markers.
MRD testing is particularly important in blood cancers such as leukemia, lymphoma, and multiple myeloma. It helps healthcare professionals evaluate how a patient responds to treatment and identify changes in disease status over time.
The development of MRD testing is connected to advances in molecular biology, flow cytometry, genetic sequencing, and laboratory diagnostics. Traditional microscopy has gradually been supplemented by more sensitive analytical methods that can identify cancer-related changes at very low levels.
Why MRD Testing Matters in Modern Healthcare
MRD testing provides additional information about cancer status that may not be visible through routine blood tests or conventional examinations. It is used in selected clinical settings to evaluate treatment response and help assess the likelihood of disease recurrence.
Its applications are particularly relevant to patients undergoing treatment for blood cancers, as well as hematologists, oncologists, pathology laboratories, and clinical research organizations.
Important clinical applications include:
Treatment Response Monitoring: Helps evaluate whether cancer-related cells remain detectable after treatment.
Disease Relapse Assessment: Can identify molecular or cellular evidence associated with returning disease.
Treatment Planning: MRD findings may contribute to decisions about additional treatment or monitoring.
Clinical Research: Supports studies evaluating new cancer treatments and therapeutic outcomes.
Long-Term Monitoring: Helps healthcare professionals follow changes in disease status over time.
MRD results are interpreted alongside other clinical findings. A negative result does not always mean that every cancer cell has disappeared, because detection depends on the test's sensitivity and the sample examined.
Major Types of MRD Testing
Different MRD testing methods identify residual cancer through cellular characteristics, genetic changes, or disease-associated molecular markers.
Flow Cytometry MRD Testing
Flow cytometry is a laboratory technique that examines individual cells using light-based measurements and specific cellular markers.
In MRD testing, laboratory specialists analyze cell populations to identify abnormal patterns associated with particular blood cancers. The technique is commonly used in leukemia and multiple myeloma monitoring.
Its sensitivity depends on the disease, sample quality, laboratory procedures, and analytical method.
Polymerase Chain Reaction (PCR) Testing
PCR-based MRD testing identifies specific genetic sequences or molecular markers associated with cancer cells.
Quantitative PCR (qPCR) and digital PCR (dPCR) are examples of technologies used in selected clinical applications. These methods can detect small quantities of disease-associated genetic material.
PCR testing is particularly useful when a suitable molecular marker has been identified.
Next-Generation Sequencing (NGS)
Next-generation sequencing analyzes genetic material to identify disease-associated sequences and mutations.
In MRD applications, NGS can detect specific genetic patterns associated with certain blood cancers. It is also used in research involving multiple myeloma and other hematological conditions.
The interpretation of sequencing results depends on the testing platform, sample characteristics, and clinical context.
Circulating Tumor DNA Testing
Circulating tumor DNA (ctDNA) testing examines small fragments of DNA released by tumor cells into the bloodstream.
This approach is increasingly studied in solid tumors and selected hematological cancers. It can provide molecular information without requiring a tissue biopsy in certain circumstances.
However, ctDNA testing and conventional MRD testing are not interchangeable in every cancer type.
MRD Testing Methods and Laboratory Processes
MRD testing involves several stages, from sample collection to laboratory analysis and clinical interpretation.
Sample Collection
The type of sample depends on the cancer and testing method. Common samples include:
Bone marrow aspirates.
Peripheral blood samples.
Tissue samples in selected applications.
Plasma samples for circulating tumor DNA analysis.
Bone marrow samples are frequently used for MRD assessment in leukemia and multiple myeloma.
Sample Preparation
After collection, laboratory professionals prepare the sample according to the selected analytical method. Preparation may involve cell separation, DNA extraction, RNA extraction, or other laboratory procedures.
Sample quality is important because damaged or insufficient material may affect test reliability.
Laboratory Analysis
Prepared samples undergo analysis using flow cytometry, PCR, sequencing, or other validated diagnostic technologies.
Laboratory instruments examine cellular or molecular characteristics to identify disease-associated signals.
Result Interpretation
Results are assessed according to the analytical sensitivity of the test, the disease being monitored, and relevant clinical guidelines.
MRD results are commonly reported as detectable or undetectable, with quantitative measurements provided when supported by the method.
Technologies and Equipment Used in MRD Testing
Modern MRD laboratories depend on specialized diagnostic instruments and molecular testing platforms.
Common technologies include:
Flow Cytometers: Analyze individual cells based on their physical and fluorescent characteristics.
PCR Systems: Amplify selected genetic sequences for molecular detection.
Digital PCR Instruments: Measure specific genetic targets through partition-based analysis.
Next-Generation Sequencing Platforms: Examine large numbers of DNA sequences.
Automated Nucleic Acid Extraction Systems: Prepare DNA and RNA for molecular analysis.
Laboratory Information Management Systems (LIMS): Support sample tracking, laboratory records, and quality management.
Bioinformatics Software: Processes sequencing information and supports genetic data interpretation.
The selection of equipment depends on the laboratory's testing capacity, clinical requirements, sample type, and validated analytical procedures.
Global MRD Diagnostic Companies and Technology Providers
The MRD testing industry includes diagnostic companies, biotechnology organizations, laboratory technology developers, and specialized clinical testing providers.
Some internationally recognized organizations involved in relevant diagnostic technologies include:
Thermo Fisher Scientific: Develops molecular biology instruments, sequencing technologies, and PCR systems.
QIAGEN: Provides molecular diagnostic technologies, sample preparation products, and genetic analysis solutions.
Bio-Rad Laboratories: Develops digital PCR, real-time PCR, and other laboratory technologies.
BD (Becton, Dickinson and Company): Provides flow cytometry instruments and cellular analysis technologies.
Agilent Technologies: Develops laboratory instruments, genetic analysis systems, and analytical technologies.
Illumina: Provides next-generation sequencing platforms and related genomic analysis technologies.
Adaptive Biotechnologies: Develops immune profiling technologies and molecular testing approaches relevant to measurable residual disease assessment.
Natera: Develops molecular residual disease testing approaches, particularly in selected solid tumor applications.
These organizations participate in different parts of the diagnostic ecosystem. Their products and technologies are not necessarily interchangeable, and not every company provides a complete MRD testing solution.
MRD Testing Regulations and Clinical Standards
MRD testing is subject to diagnostic laboratory regulations and quality requirements that vary by country and test type.
In the United States, the Food and Drug Administration (FDA) regulates applicable diagnostic devices and certain molecular testing products. The Centers for Medicare & Medicaid Services (CMS) oversees relevant laboratory requirements under the Clinical Laboratory Improvement Amendments (CLIA).
In India, the Central Drugs Standard Control Organization (CDSCO) regulates applicable medical devices and in-vitro diagnostic products. The National Accreditation Board for Testing and Calibration Laboratories (NABL) provides laboratory accreditation based on relevant quality standards.
Internationally, the International Organization for Standardization (ISO) provides standards such as ISO 15189 for medical laboratory quality and competence.
Important quality requirements include:
Analytical sensitivity and specificity.
Sample identification and traceability.
Laboratory equipment validation.
Quality control and documentation.
Personnel competency.
Data security and patient confidentiality.
Standardized reporting procedures.
Clinical interpretation should follow disease-specific guidelines and established medical protocols.
Recent Developments in MRD Testing, 2024–2026
MRD diagnostics continue to develop through improvements in molecular detection, genomic analysis, and laboratory automation.
Next-Generation Sequencing: NGS technologies continue to support sensitive detection of disease-associated genetic sequences in selected blood cancers.
Digital PCR: Digital PCR platforms are being used in research and clinical applications requiring precise measurement of low-abundance genetic targets.
Liquid Biopsy Development: Circulating tumor DNA research is expanding the potential applications of molecular residual disease assessment in solid tumors.
Artificial Intelligence: Computational approaches are being explored to assist with sequencing analysis, biomarker identification, and interpretation of complex diagnostic information.
Automated Laboratory Systems: Integrated sample preparation, analysis, and information management technologies are helping laboratories organize complex diagnostic workflows.
These developments are expanding the scientific understanding of MRD testing, although clinical availability and validated applications differ across diseases and healthcare systems.
Frequently Asked Questions About MRD Testing
1. What is MRD testing in cancer?
MRD testing detects very small amounts of cancer cells or disease-associated molecular markers that may remain after treatment. It is particularly important in monitoring certain blood cancers.
2. What are the main types of MRD testing?
Common methods include flow cytometry, quantitative PCR, digital PCR, next-generation sequencing, and circulating tumor DNA analysis.
3. Is MRD testing performed using blood or bone marrow?
Both sample types may be used. Bone marrow is commonly used in leukemia and multiple myeloma, while blood-based testing is appropriate in selected clinical situations.
4. What does MRD-negative mean?
MRD-negative means that the test did not detect measurable disease within its specified sensitivity. It does not necessarily establish that every cancer cell has disappeared.
5. Which companies develop MRD testing technologies?
Organizations involved in relevant technologies include Thermo Fisher Scientific, QIAGEN, Bio-Rad, BD, Illumina, Adaptive Biotechnologies, Agilent Technologies, and Natera.
Conclusion
MRD testing is an important development in modern cancer diagnostics, particularly for monitoring leukemia, lymphoma, and multiple myeloma. Flow cytometry, PCR, next-generation sequencing, and circulating tumor DNA technologies provide different approaches to identifying residual disease. Advances in laboratory automation and molecular analysis continue to expand the applications of these methods. MRD results must be interpreted alongside other clinical information and disease-specific medical guidelines.