What Does Minimal Residual Disease Mean?

This page is for people with a blood cancer, and their families, who see an MRD result on a report. It explains what the numbers mean, how the test is done, and what a negative result does and does not settle.

A pathologist reads a bone marrow slide under a microscope. At best, they can spot about one cancer cell among 100 normal ones. The FDA states that limit plainly. Standard visual detection in blood cancers has a threshold of one tumor cell in 100 cells.

So "complete remission" has always meant something narrower than it sounds. It means nothing visible at 1 in 100.

MRD testing works far below that.

MRD results come as a fraction or as a negative power of ten. Translate them:

• 10⁻⁴ — 1 cancer cell in 10,000, the same as 0.01%
• 10⁻⁵ — 1 in 100,000
• 10⁻⁶ — 1 in 1,000,000

A result of "MRD negative at 10⁻⁵" does not mean zero cells. It means none were found at a sensitivity of one in 100,000. That sensitivity is part of the result. Always ask which level was used.

The guidance recognizes four platforms:

• Flow cytometry — tags cells with glowing markers, then sorts them by the proteins on their surface
• Next-generation sequencing — reads DNA or RNA to find the tumor's own unique sequence
• RT-qPCR — copies and counts one specific fusion gene signal
• ASO-PCR — copies and counts one exact known sequence

The FDA says it does not favor one platform. It says drug sponsors should set out the choice in advance. That matters for you too. Results from different platforms may not be directly comparable. Ask whether follow-up testing will use the same method as your first test.

Here is a detail worth borrowing. The FDA says a test's detection floor should sit at least 10-fold below the level used for decisions. If a decision is made at 1 × 10⁻⁵, the test should reach 1 × 10⁻⁶ where possible.

The reason is simple. A test working right at its own limit gives shaky answers at the exact point you care about.

There is no single MRD cutoff. The FDA guidance discusses each disease separately.

Acute lymphoblastic leukemia. The FDA has accepted an MRD level of 0.1% or more as a marker of high relapse risk. That applies to patients in a first or second complete remission. In relapsed or refractory ALL (leukemia that came back or did not respond to treatment), levels under 0.01% have been accepted as supporting evidence that a drug works.

Acute promyelocytic leukemia. An MRD level below 0.01% is generally counted as negative here. That applies after first-line induction (the first phase of treatment) built on arsenic and tretinoin, or on idarubicin and tretinoin. When drugs that push cells to mature are used, the FDA prefers testing at the end of consolidation (the next phase, meant to clear remaining cells) rather than after induction. This helps avoid false-positive results.

Chronic lymphocytic leukemia. The FDA says the test's lowest detectable level should be below 10⁻⁴, which is 0.01%. It says MRD should be measured in patients who are in complete response.

Chronic myeloid leukemia. CML uses a different yardstick, the International Scale. Major molecular response means BCR-ABL below 0.1% on that scale. The FDA advises PCR tests sensitive to more than a 4.5-log reduction, meaning they can detect a very large drop in the signal.

Acute myeloid leukemia. The FDA prefers testing at complete response, once blood counts have recovered. There is an extra step here. Drug sponsors should show that the markers reflect real leukemia. They should rule out clonal hematopoiesis, a blood cell change that is not leukemia.

The FDA names bone marrow as the preferred sample for ALL, AML, and APL. In drug trials, blood can be used when the choice is justified. Other blood cancers may use other samples, so ask which one applies to you.

In multiple myeloma the FDA's draft guidance is firmer. It says a bone marrow aspirate (liquid marrow drawn with a needle) is required to determine MRD negativity.

So for these cancers, an MRD check can mean another marrow procedure. If your MRD is being followed, ask how often marrow will be sampled.

In multiple myeloma, the FDA's January 2026 draft guidance lays out specifics. It is a draft, not final:

• A threshold of at least 1 in 10⁵ residual tumor cells, so one cell in 100,000
• Flow cytometry or sequencing-based methods
• Bone marrow aspirate required
• The patient must first reach complete response or stringent complete response
• MRD checked at that point, or within a set window such as plus or minus 3 months

The FDA also records a vote. At an April 2024 meeting, its Oncologic Drugs Advisory Committee agreed unanimously that MRD is acceptable as an endpoint, a measure used to judge whether a drug works in a trial. It can support accelerated approval of drugs for multiple myeloma.

Sustained MRD negativity means staying negative over time. That is a different measure. The FDA notes limited data on it, and says it may be used as a secondary or exploratory measure.

MRD is strongest in combination, not alone. NCI's clinician summary for childhood ALL shows the range. Gene findings combined with MRD can define groups with event-free survival above 95%. Event-free survival is the share of people with no relapse or other major event over a set time. The same pairing defines other groups with event-free survival of 50% or lower.

Two cautions belong with any negative result. First, the FDA notes that in chronic lymphocytic leukemia, leftover disease can sit in the bone marrow, blood, lymph nodes, liver, and spleen. So where the sample comes from matters. Second, in myeloma the FDA draft says MRD should be justified for the specific group of patients. It says there are not yet enough data to use MRD this way for maintenance treatment, smoldering myeloma or MGUS.

So a negative MRD is good news about one sample, at one sensitivity, on one date. It does not by itself end follow-up. Your team decides what comes next.

• Which platform was used, and at what sensitivity was the result reported?
• Was this bone marrow or blood?
• What threshold is my team using to make decisions, and where does my result fall?
• Will the next test use the same assay, so the numbers can be compared?
• Does an MRD result here change my treatment, or is it being tracked for information?

Remission and Recurrence covers the wider vocabulary. What Does Circulating Tumor DNA Mean? covers a related blood test. Questions to Ask at End of Treatment helps with what comes next.

• U.S. Food and Drug Administration — Hematologic Malignancies: Regulatory Considerations for Use of Minimal Residual Disease in Development of Drug and Biological Products for Treatment
• U.S. Food and Drug Administration — Minimal Residual Disease and Complete Response in Multiple Myeloma: Use as Endpoints to Support Accelerated Approval (draft guidance, January 2026)
• NCI PDQ — Childhood Acute Lymphoblastic Leukemia Treatment (Health Professional Version)