Myelodysplastic Syndrome (MDS): Understanding Your Pathology Report

Section Editor: David Li MD
June 27, 2026

Myelodysplastic syndrome (MDS) is a group of blood cancers that affect the bone marrow, the spongy tissue inside bones where new blood cells are made. In MDS, the bone marrow produces blood cells that do not develop or function properly, so many are destroyed before they can do their job. As a result, people with MDS often have low numbers of healthy blood cells. MDS also increases the risk of developing acute myeloid leukemia (AML), a faster-growing blood cancer, although not everyone with MDS develops it. In the most recent World Health Organization classification, this group of diseases is also referred to as myelodysplastic neoplasms, but the abbreviation MDS is still used.

This article will help you understand the findings in your pathology report for myelodysplastic syndrome, what each term means, and why it matters for your care.

What cells are normally found in the blood?

Normal blood contains several types of cells, each with an important role:

Red blood cells carry oxygen from the lungs to the rest of the body.
White blood cells, including neutrophils, lymphocytes, and monocytes, are part of the immune system and fight infection.
Platelets help stop bleeding by forming clots after an injury.

These cells are made in the bone marrow through a process called hematopoiesis. In myelodysplastic syndrome (MDS), this process is disrupted, which leads to fewer healthy cells being produced.

What are the symptoms of myelodysplastic syndrome?

The symptoms of myelodysplastic syndrome (MDS) depend on which blood cells are low. Many people have no symptoms at first and are diagnosed after a routine blood test shows low counts.

Anemia (low red blood cells) — May cause fatigue, weakness, shortness of breath, or chest pain.
Neutropenia (low neutrophils) — Makes infections more likely and sometimes more severe.
Thrombocytopenia (low platelets) — Increases the risk of bruising and bleeding.
Pancytopenia (all three cell types low) — Can cause a combination of the symptoms above.

What causes myelodysplastic syndrome?

Myelodysplastic syndrome (MDS) begins when a genetic change develops in an immature bone marrow cell. This change is usually not inherited but happens during a person’s life. As the abnormal cell multiplies, it produces more cells with the same change, which gradually replace the healthy cells in the bone marrow. As MDS progresses, additional genetic changes may appear, which can make the disease more advanced or more likely to transform into acute myeloid leukemia.

Most cases occur on their own with increasing age, but the risk is higher in people who have previously received chemotherapy or radiation therapy for another cancer. When MDS develops after these treatments, it is classified separately as a therapy-related myeloid neoplasm, which tends to behave less favorably. Rarely, an inherited predisposition runs in families.

How is the diagnosis made?

The diagnosis of myelodysplastic syndrome (MDS) usually begins when a blood test shows low numbers of one or more types of blood cells. A blood smear, a thin layer of blood examined under a microscope, may show cells that are abnormal in size, shape, or appearance. To confirm the diagnosis, a bone marrow biopsy and aspiration are performed, in which small samples of bone marrow are removed and examined by a pathologist.

The pathologist looks for abnormal cell development (described in the next section), counts the proportion of immature cells, called blasts, and uses an iron stain to detect ring sideroblasts. A karyotype and, in many cases, next-generation sequencing (NGS) are performed to detect chromosomal and gene changes, which help classify the disease and guide treatment. Because several other conditions can cause low blood counts or abnormal-looking cells, the diagnosis is made only after these other causes (described later in this article) have been ruled out.

What does myelodysplastic syndrome look like under the microscope?

When examining the bone marrow in myelodysplastic syndrome (MDS), the pathologist looks for dysplasia, which means cells that are abnormal in shape, size, or color. When only one type of blood cell looks abnormal, it is called single-lineage dysplasia; when two or more types look abnormal, it is called multilineage dysplasia. To support a diagnosis of MDS, at least 10% of the cells in a given cell type must show dysplasia.

The pathologist also looks for two other important features. Ring sideroblasts are immature red blood cells with excess iron that forms a ring around the nucleus and is seen on a special iron stain. Blasts are very immature cells that normally develop into mature blood cells; counting the percentage of blasts is important because a higher number suggests the disease may be moving closer to acute leukemia.

What genetic changes and chromosome abnormalities are found in MDS?

Genetic testing is an essential part of evaluating myelodysplastic syndrome (MDS). A karyotype examines the chromosomes (the structures that hold DNA) for missing or extra pieces. Some chromosome changes, such as an isolated deletion of part of chromosome 5 (called del(5q)), are associated with a better outlook and a good response to specific treatments, while others, such as loss of chromosome 7, are associated with a higher risk. When three or more abnormalities are found together, this is called a complex karyotype and usually indicates higher-risk disease.

Next-generation sequencing detects smaller gene mutations that cannot be seen on a karyotype. Mutations in genes such as SF3B1, TP53, ASXL1, SRSF2, and RUNX1 are common in MDS. Some of these directly affect classification and prognosis; for example, an SF3B1 mutation is linked with a more favorable outlook, while changes affecting both copies of the TP53 gene are linked with higher-risk disease. Your report will list any chromosome or gene changes that were found.

What are the types of myelodysplastic syndrome?

Doctors classify myelodysplastic syndrome (MDS) into types based on the appearance of the cells, the number of blasts, and the genetic changes present. In the most recent World Health Organization classification, the types are grouped in two ways.

Types defined by a specific genetic change:

MDS with low blasts and isolated del(5q) — Defined by the loss of part of chromosome 5. It generally has a favorable outlook and often responds to a specific medication.
MDS with low blasts and an SF3B1 mutation — Usually associated with ring sideroblasts and a more favorable outlook.
MDS with biallelic (two-copy) TP53 inactivation — Defined by changes affecting both copies of the TP53 gene. This is a higher-risk type with a greater chance of progressing to acute leukemia.

Types defined by the appearance of the cells and the number of blasts:

MDS with low blasts — Dysplasia is present, but the number of blasts is not increased.
Hypoplastic MDS — The bone marrow contains fewer cells than expected.
MDS with increased blasts — Divided into MDS-IB1 (5 to 9% blasts in the bone marrow, or 2 to 4% in the blood) and MDS-IB2 (10 to 19% blasts in the bone marrow, or 5 to 19% in the blood, or the presence of structures called Auer rods). If blasts reach 20% or more, the diagnosis changes from MDS to acute myeloid leukemia.
MDS with fibrosis — Scarring is present in the bone marrow, which is associated with a higher risk.

You may see older terms on your report, such as “MDS with single or multilineage dysplasia,” “MDS with ring sideroblasts,” or “MDS with excess blasts (MDS-EB).” These describe the same diseases using the previous classification system and may still appear during the transition to the newer terms.

Are some forms of MDS inherited?

Most people who develop myelodysplastic syndrome (MDS) do not have an inherited risk, and these cases are called sporadic. Rarely, some people inherit genetic changes (germline mutations) that increase the risk of MDS or other bone marrow diseases. If other family members have had similar conditions or persistent low blood counts, your doctor may recommend genetic testing to look for an inherited cause.

What is the prognosis for myelodysplastic syndrome?

The outlook for myelodysplastic syndrome (MDS) varies widely. Some people have mild disease that remains stable for years, while others have higher-risk disease that progresses more quickly. About 30% of people eventually develop acute myeloid leukemia. To estimate risk and guide treatment, doctors use scoring systems, most commonly the Revised International Prognostic Scoring System (IPSS-R) and the newer molecular version (IPSS-M), which combine the number of blasts, chromosomal changes, the degree of low blood counts, and gene mutations. These scores sort MDS into lower-risk and higher-risk groups. A complex karyotype and changes affecting both copies of the TP53 gene are among the features linked with a higher risk. Your prognosis depends on your own combination of these factors, which your care team can explain in the context of your specific report.

What happens after a diagnosis of myelodysplastic syndrome?

After myelodysplastic syndrome (MDS) is diagnosed, the risk score helps guide treatment, which differs for lower- and higher-risk disease. The pathology and genetic findings shape several decisions:

Supportive care — Blood transfusions for anemia or low platelets, treatment of infections, and medicine to remove excess iron when many transfusions are needed.
Treatment of anemia (lower-risk disease) — Medicines that stimulate red blood cell production (erythropoiesis-stimulating agents) and a drug called luspatercept can reduce the need for transfusions.
Lenalidomide — Particularly effective for MDS with an isolated del(5q) change.
Hypomethylating agents (higher-risk disease) — Drugs such as azacitidine and decitabine can improve blood counts and delay progression to leukemia.
Stem cell (bone marrow) transplant — An allogeneic transplant, using blood-forming cells from a donor, is the only treatment that can cure MDS and is generally considered for higher-risk patients who are well enough.

Care is provided by a hematology team, and regular blood tests and follow-up help monitor the disease. Clinical trials of newer treatments may also be an option to discuss. Decisions about treatment are made by the care team together with the patient, based on the specific findings in the report.

Other conditions that can look like MDS

Several other conditions can cause low blood counts or abnormal-looking blood cells and must be ruled out before confirming myelodysplastic syndrome (MDS). These include vitamin B12 or copper deficiency, certain medications, alcohol use, heavy metal poisoning, infections, and autoimmune diseases. Other bone marrow cancers, such as chronic myelomonocytic leukemia, can also resemble MDS. Your doctor reviews your history and test results carefully to rule out these possibilities.

Questions to ask your doctor

What type of MDS do I have?
What did my chromosome and gene tests show, and how do they affect my outlook?
Am I considered lower- or higher-risk, and which scoring system was used?
Do I have excess blasts, and what does that mean for my risk of developing acute leukemia?
Do I have any of the changes that affect treatment, such as del(5q), an SF3B1 mutation, or a TP53 change?
Will I need blood transfusions, and how will iron levels be managed?
What treatment options are available for me, and what are their benefits and side effects?
Could I benefit from a medication to improve my blood counts?
Should I be evaluated for a stem cell transplant?
Should my family members be tested for inherited conditions related to MDS?
Are there clinical trials that I should consider?