TYPES OF MDS

Myelodysplastic syndromes (MDS) involve ineffective blood cell production.⁴ All blood cells — red blood cells, white blood cells and platelets — are produced in the bone marrow. With MDS, fewer "good" blood cells circulate in the bloodstream, which can lead to abnormally low amounts of any of these blood cells.

There are two main classifications healthcare professionals use to determine the type of MDS a person has: The French-American-British (FAB) classification system and The World Health Organization (WHO) classification system.^7,8

FAB was developed at an international conference with doctors from France, the United States and Britain. The classification allows doctors to determine a patient’s prognosis with myelodysplastic syndromes. The World Health Organization (WHO) developed its tool to better classify patients with MDS.

The FAB classification uses the following categories:

FAB Classification7
Type of MDS	Percent of blasts in marrow (less than 5% is normal)
Refractory Anemia (RA)	Less than 5% blasts in bone marrow (normal count)
Refractory Anemia with Ringed Sideroblasts (RARS)	Less than 5% blasts in bone marrow (normal amount), plus more than 15% of abnormal red blood cells called ringed sideroblasts
Refractory Anemia with Excess Blasts (RAEB)	5 to 20% blasts in bone marrow
Refractory Anemia with Excess Blasts in Transformation (RAEB-t)	21-30% blasts in bone marrow
Chronic Myelomonocytic Leukemia (CMML)	5% to 20% blasts in bone marrow, plus a large number of a type of white blood cell called monocytes

The WHO classification uses the following categories:

WHO Classification8
Types of MDS	Percent of blasts in bone marrow (<5% is considered normal)
Refractory Anemia (RA)	Less than 5% blasts in bone marrow
Refractory Anemia with Ringed Sideroblasts (RARS)	Less than 5% blasts in bone marrow Greater than or equal to 15% ringed sideroblasts
Refractory Cytopenia with Multilineage Dysplasia (RCMD)	Less than 5% blasts in bone marrow Less than 15% ringed sideroblasts 2 or more abnormal blood cells lines in bone marrow
Refractory Cytopenia with Multilineage Dysplasia and Ringed Sideroblasts (RCMD-RS)	Less than 5% blasts in bone marrow Greater than or equal to 15% ringed sideroblasts 2 or more abnormal blood cells lines in bone marrow
Refractory Anemia with Excess Blasts-1 (RAEB-1)	5-9% blasts in bone marrow 0-4% blasts in blood
Refractory Anemia with Excess Blasts-2 (RAEB-2)	10-19% blasts in bone marrow 5-19% blasts in blood
Myelodysplastic Syndrome, unclassified (MDS-U)	Less than 5% blasts in bone marrow Abnormal white cells or platelets
Myelodysplastic Syndromes Associated with Isolated del(5q)	Less than 5% blasts in bone marrow 0-4% blasts in blood Chromosomes with partial loss of chromosome #5

A third MDS-related scoring system, the International Prognostic Scoring System (IPSS) is used to describe the risk that a patient’s disease will develop into Acute Myeloid Leukemia. The IPSS score is based on three factors:⁷

	Percent of blasts in the bone marrow
	If the patient has 1 or more cytopenias – low red, white and/or platelet blood cell counts
	Changes in bone marrow blood cell chromosomes (cytogenetics)

International Prognostic Scoring System for MDS9
	Score Value
Prognostic Variable	0.0	0.5	1.0	1.5	2.0
Bone Marrow Blasts (%) (immature blood cells)	<5	5-10	—	11-20	21-30
Cytogenetics* (profile of chromosomal abnormalities)	Good	Intermediate	Poor
Cytopenias (low red, white and/or platelets cell count)	0/1	2/3

^*Good = normal, -Y alone, del (5q) alone, del (20q) alone; Poor = complex (≥ 3 abnormalities) or chromosome 7 anomalies; Intermediate = other abnormalities.

Prognostic Score and IPSS Subgroup
Prognostic Score	IPSS Subgroup
0	Low
0.5-1.0	Intermediate-1
1.5-2.0	Intermediate-2
>2.5	High

As the MDS disease progresses from low to high risk, there is a greater likelihood for patients’ disease to develop into AML or death.

blasts = immature blood cell
sideroblasts =ring shaped iron deposit on red blood cell

To learn more about the steps to understand a FAB, WHO or IPSS diagnosis, Click here.

References