Understanding MDS Sub-types
A guide to the sub-types of Myelodysplastic Syndromes (also called Myelodysplastic Neoplasms) and why your sub-type matters.
Myelodysplastic Syndromes (MDS) is a complex condition
Myelodysplastic Syndromes (MDS) are a group of rare bone marrow disorders classified by the World Health Organisation (WHO) as a type of blood cancer. ‘Myelo’ refers to the bone marrow, ‘dysplastic’ means abnormal or faulty, and ‘syndrome’ denotes a group of related symptoms.
Changing terminology
The WHO – and some healthcare professionals – have recently begun to use the term ‘neoplasms’ rather than ‘syndromes’, as they feel this describes the condition more accurately, meaning your MDS may be referred to as a myelodysplastic neoplasm or ‘MDN’ by some doctors.
From pre-leukaemia to recognised cancer
MDS used to be called a ‘pre‑leukaemic’ condition, although only around 30% of people with MDS go on to develop acute leukaemia. Today it is classed as a cancer in its own right because the faulty cells behave in the same way as cells in other more common types of blood cancer - replicating themselves and increasing in number, potentially crowding out healthy cells.
Why MDS behaves differently in everyone
Each patient may have some or all symptoms, to varying degrees. This is why MDS is a complex condition – it behaves differently in each person depending on their own individual make-up, with factors such as general health, genetics and other medical conditions also coming into the equation. Understanding these differences helps clinicians plan the best approach for each patient.
In short: Myelodysplastic Syndromes (MDS) are a group of rare blood cancers that affect how bone marrow makes blood cells. They are complex and vary from person to person, which is why understanding your specific sub-type is so important.
What is an MDS sub-type?
An MDS sub-type is a specific form or category of Myelodysplastic Syndrome (MDS).
While everyone with MDS has problems with how their bone marrow makes blood cells, the exact pattern of those problems varies from person to person.
Why knowing your sub-type matters
Knowing your sub-type can help you understand how your disease may develop, and why certain treatments are being given or considered. Pinpointing a patient’s specific type of MDS is a science that’s improving all the time through genetic research, better data analysis, and even the use of artificial intelligence (AI).
Did you know?
26% of UK patients (2024 MDS Global Survey) said they did not know their sub-type.
How doctors classify MDS sub-types
There is a system, managed by the World Health Organisation (WHO), for classifying the different types of MDS.
The system is reviewed every few years as more is learned about the disease.
Another classification — from the International Consensus Classifications (ICC) — is similar to the WHO’s but less widely used.
Both systems aim to create a universal language for doctors and researchers working with MDS.
How your sub-type is identified
Your sub-type is determined by analysing:
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Blood test results
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The ratio of immature stem cells (blasts) to healthy cells in your bone marrow
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Chromosomal or genetic changes found in specialised tests
MDS may be suspected if your blood tests show consistently low or falling blood counts in one or more cell types, but further tests are needed for a confirmed diagnosis.
The testing process
A bone marrow biopsy shows the percentage of immature blood stem cells (blasts) that haven’t developed into healthy cells.
The sample is sent to a specialised laboratory for genetic testing, which is why it can take six weeks or more after diagnosis to get a full picture of your sub-type and prognosis. Once your healthcare team understands what’s happening in your bone marrow and at a genetic level, they can decide on the best course of treatment for you as an individual.
Current MDS sub-types (October 2025)
The following subtypes are recognised by WHO/ICC classifications. Click each name to expand for a clear summary.
MDS SLD — MDS with single lineage dysplasia
In this sub-type, only one type of blood cell is affected, so either red blood cells, white blood cells or platelets.
MDS MLD — MDS with multi-lineage dysplasia
Two or more blood cell types are affected, although this can be to differing levels, with one cell type more affected than another.
MDS RS — MDS with ring sideroblasts
A sideroblast is a young blood cell whose job it is to manufacture haemoglobin, but ring sideroblasts have developed a distinctive ring of iron granules which interferes with this process. MDS-RS is recognised as a slower-developing form of MDS with low risk of progressing to AML, but it can be resistant to treatments designed to relieve anaemia.
MDS RA — MDS with refractory anaemia
Refractory anaemia is an inherited form of anaemia with no specific cause identified. It can be highly resistant to treatment, with any relief from the symptoms of anaemia tending to be short-lived.
MDS RARS — Refractory anaemia with ring sideroblasts
Both refractory anaemia and ring sideroblasts (see above) are present.
MDS EB / MDS IB — MDS with excess or increasing blasts
May be sub-divided into MDS-EB-1 and MDS-EB-2 (or MDS IB1 & MDS IB2, with ‘I’ standing for ‘increasing’). Refers to the ratio of immature blood stem cells (blasts) that have failed to develop into normal, healthy blood cells, and remain in the bone marrow. EB or IB 1 means 4-9% of blasts are present, where EB or IB 2 indicates 10-19% of blasts. Over time these blast cells can begin to crowd out potentially healthy cells.
MDS del (5q) and MDS with Isolated del (5q)
A specific, common sub-type of MDS, where part of chromosome five has found to be missing, or ‘deleted’. If the term ‘isolated’ is used, it means this is the only chromosome deletion found, where in some sub-types there may be other deletions present in addition to 5q.
MDS F — MDS with Fibrosis
MDS with fibrosis in the bone marrow. Scar-like tissue is present in the bone marrow, making it difficult for new blood stem cells to develop and grow.
MDS H — Hypoplastic Myelodysplasia
A rare but distinctive form of MDS with very specific characteristics, and which can particularly affect younger people. The bone marrow appears sluggish and produces fewer cells.
MDS/AML
MDS with blasts higher than 10% but less than 20% (over 20% blasts is deemed Acute Myeloid Leukaemia, or AML). As this is considered high risk for progressing to AML, treatments normally reserved for AML may be used to slow down the progression of the disease.
MDS U — MDS with unclassifiable sub-type
Sub-type unclear at diagnosis, or tests have been inconclusive. Will need ongoing monitoring, then further tests at a later stage may clarify sub-type of MDS.
MDS/MPN — MDS with myeloproliferative neoplasms
Also referred to as ‘overlap disease’. Has characteristics of both MDS and MPN, with the most common MPN being CMML (Chronic Myelomonocytic Leukaemia). Broadly speaking, MPNs produce too many blood cells, where MDS produces faulty cells.
‘Sub-types’, ‘prognosis’ and IPSS scores — what does it all mean?
Understandably, in just about every case the first thing a person asks after diagnosis and upon hearing the words ‘blood cancer’ is, “what’s my prognosis?”. The difficult truth is, no two patients’ MDS is the same or will develop in the same way. Some types of MDS need little intervention other than regular monitoring, and can remain relatively stable for years, even decades, where other types progress more quickly.
To get the most accurate picture of how an individual patient’s particular disease is likely to progress the following factors must be taken into consideration:
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The patient’s MDS sub-type and genetic make-up
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Their general health
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Their age and any frailty
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Other known conditions and treatments
About the International Prognostic Scoring System (IPSS)
Clinicians calculate the most likely outcome and progression by using a process called the International Prognostic Scoring System (IPSS), which helps to categorise disease risk levels (‘risk’ in this case referring to the risk of progressing to AML). First developed in 1997, the system is reviewed periodically as new data and information becomes available.
IPSS-R relates to the first full revision (‘R’ simply stands for ‘revised’) and is the system most often used today. The newest version, IPSS-M (for ‘molecular’), developed in 2022, is now increasingly used by clinicians to help assess disease risk more precisely.
Important points to remember: your ‘score’ or ‘risk level’ is calculated using median survival data from different countries with differing treatment regimes. Also, as MDS tends mostly to affect older people, many will have suffered from other, non-related conditions that could have affected survival post-MDS diagnosis. In short, low, intermediate or high risk can mean different things in different people. Your clinical team know you and your physiology best, and are the best-placed people to give you your personal prognosis, which can change over time with treatment and/or supportive care, or if general health improves or worsens.
Summary - The International Scoring Systems
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IPSS — established 1997; estimates risk from blasts, cytogenetics, blood counts
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IPSS R — commonly used revised version with refined risk categories (R stands for revision)
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IPSS M (2022) — incorporates molecular (genetic) information; now increasingly used by clinicians
Important: Scores come from population data and can mean different things for different people. Your clinical team knows your overall health best and will provide personalised guidance that can change with treatment and time.
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Low risk: may need monitoring and supportive care
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Intermediate risk: may require active treatment
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High risk: more likely to progress to AML; treatment aims to reduce that risk
Your MDS is unique to you - stay positive and focus on your well being
Although it is good to connect with other people with a similar condition and get tips and ideas from them as to how to cope with the symptoms, your particular MDS is unique to you, and just because one person may have certain symptoms or treatments does not necessarily mean it will be the same for you.
Try to stay positive, look after your general health as much as you can, and remember that research into MDS is ongoing. There are teams of MDS specialists, both in the UK and around the world, who meet up regularly and share knowledge and resources to try and find better treatments and improve outcomes.
Further information and resources
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You can download our comprehensive MDS Patient Guide for clear, reliable information about living with MDS and understanding your diagnosis.
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Find out how MDS is treated and what options might be right for you on our MDS Treatments page
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You don’t have to face MDS alone — explore our Support section for practical advice and emotional support via our support line and virtual meetings.
