If you’re looking for a subject with complicated language and jargon that’s hard for the everyday person to understand, look no further than myeloproliferative neoplasms (MPNs). Between MPNs and myelodysplastic syndrome (MDS), it’s easy to be confused by the complex names of blood cancers and their related conditions.

This article will explain the terminology, history, and differences between MPNs and MDS. By the end, you’ll have a better understanding of the terms for your condition, and hopefully have an easier time discussing it with doctors and loved ones alike.

What Are Myeloid Cells?

To get a grip on MPNs and MDS, it’s important to first understand how blood cells form in your body. Blood cells form in the bone marrow (the spongy tissue inside your bones), where they have the potential to become different types of cells. There are two main types of blood cells — myeloid and lymphoid.

Myeloid cells form erythrocytes (red blood cells), platelets, and certain types of white blood cells. Lymphoid cells go on to become other types of white blood cells known as B cells and T cells. Both MPNs and MDS develop due to errors in blood cell formation from myeloid blood cells.

What Are Myeloproliferative Neoplasms?

MPNs are a group of chronic blood cancers that occur when your bone marrow makes too many blood cells. You may have too many of one or several blood cell types, depending on which MPN you have.

In 1845, chronic myeloid leukemia (CML) was the first MPN to be identified. Over time, doctors and researchers identified other MPNs, including:

• Primary myelofibrosis (PMF) in 1879
• Polycythemia vera (PV) in 1882
• Essential thrombocythemia (ET) in 1903

While these diseases were known separately, it wasn’t until 1951 that hematologist William Dameshek saw their connection and coined the term “myeloproliferative disorders” to describe them together. This term is still in use today, but it’s more common to hear them referred to as MPNs.

Here’s a breakdown of the complex medical terms used to describe MPNs and MDS.

”Myeloproliferative“ refers to rapid growth related to the bone marrow, where blood cells are formed. Neoplasms are new growths in your body that aren’t controlled by normal cell division. A neoplasm may be malignant (cancerous) or benign (noncancerous).

The term ”myelodysplastic“ refers to abnormal growth related to the bone marrow, meaning immature blood cells that don’t properly develop into healthy blood cells.

Simply put, in MPNs there is faster, uncontrolled production of too many blood cells. In MDS, there are less blood cells because the myeloid cells don’t mature into healthy cells.

The Continued Evolution of MPNs

As doctors and researchers have continued to learn more about MPNs and MDS, the conditions’ classifications have changed over time. The umbrella term “myeloproliferative disorders” originally referred to CML, ET, PMF, and PV.

The World Health Organization (WHO) has updated the classification of blood cancers to further divide MPNs based on the mutations (gene changes) in cancer cells. In the fifth edition of the WHO diagnostic criteria, available since 2022, there are eight types of MPNs.

Chronic Myeloid Leukemia

CML is defined by the presence of the Philadelphia chromosome on cancer cells. This is a mutation made from two broken chromosomes fused together. This fusion produces the BCR-ABL1 gene, which causes bone marrow cells to grow and divide uncontrollably.

Essential Thrombocythemia, Primary Myelofibrosis, and Polycythemia Vera

ET, PMF, and PV do not have the Philadelphia chromosome, but they may have other gene mutations. These include CALR, Janus kinase 2 (JAK2), and MPL mutations. These changes cause bone marrow cells to grow and divide uncontrollably.

Learn more about JAK2 mutations and MPNs.

New Types of MPNs

In addition to the original MPNs defined in 1951, the WHO has also added:

• Chronic eosinophilic leukemia (CEL)
• Chronic neutrophilic leukemia (CNL)
• Juvenile myelomonocytic leukemia (JMML)
• Myeloproliferative neoplasm, not otherwise specified (MPN-NOS)

CEL and CNL are diagnosed if your bone marrow produces too many of certain types of white blood cells known as eosinophils or neutrophils. Eosinophils are involved in allergic responses and protect your body from parasitic infections. Neutrophils trap bacteria and ingest them.

JMML is a blood cancer of early childhood which involves uncontrolled production of monocytes, a type of immune cell, in the bone marrow. The term MPN-NOS describes cases in which a person has an increased blood cell production rate, but they don’t meet the specific diagnostic criteria of any MPN listed above.

Prefibrotic Primary Myelofibrosis vs. Essential Thrombocythemia

The WHO added prefibrotic-PMF to its MPN classification system in 2016. A common symptom of prefibrotic-PMF is thrombocytosis, or a high platelet count. ET also causes a high platelet count, so if you have had ET for some time, there’s a chance you may have been misdiagnosed under the older guidelines. In fact, one study of over 1,000 people originally diagnosed with ET found about 20 percent actually met the criteria for pre-PMF instead.

It’s important that you receive the correct diagnosis because prefibrotic-PMF is much more likely to progress into acute myeloid leukemia (AML) than ET. If you were previously diagnosed with ET, your doctor or hematologist may want to run new tests and reevaluate your disease.

Learn more about how and why MPNs transform into AML.

What Are Myelodysplastic Syndromes?

Myelodysplastic syndromes are a group of blood cancers caused by immature blood cells. These immature cells — known as blasts — can’t function properly and die in the bone marrow or shortly after they enter your bloodstream.

With so many immature blood cells in your bone marrow, you can’t make enough healthy blood cells. As a result, you may be at a high risk of anemia (low red blood cell count), infections, or easy bleeding.

The type of MDS you have depends on several factors. The latest WHO classification divides MDS into categories based on:

• How your red blood cells, white blood cells, and platelets look under a microscope
• What portion of your early red blood cells are ring sideroblasts (cells with rings of iron around the center)
• What gene mutations are present in your bone marrow

Because the differences between these types can be so small, it can be hard for doctors to tell which MDS someone has.

Overlap Between MPNs and MDS

To make matters even more confusing, it’s possible to have an MDS/MPN overlap disorder. This means the disease has characteristics of both an MDS and an MPN.

Getting the Correct Diagnosis

When it comes to making an accurate diagnosis, doctors and hematologists have to rule out other conditions using a series of tests. Examples include:

• Blood counts to measure your red blood cell, white blood cell, and platelet counts
• A peripheral blood smear to check the number and shape of your blood cells
• Karyotyping, a type of genetic study, to look for abnormal cytogenetics like Philadelphia chromosomes or other mutations
• A bone marrow biopsy to look at immature blood cells and check for fibrosis

Getting the correct tests will help you get the right diagnosis and enable your doctor to accurately predict your risk factors and recommend the right treatment option. Read more about the value of consulting an MPN specialist — even once.

Explaining Your Condition to Others

No one understands living with a complex medical condition better than you. When sharing your experiences with your loved ones or others in your life, remember that they don’t have all the same information you do. Encourage them to read more articles and educate themselves on MPNs.

When explaining what an MPN is to a loved one, break it down into simple terms. They may not know much about medicine and science, so start from the basics. A simple way to explain an MPN may be, “My blood cells have genetic changes that cause them to grow out of control.” Depending on the specific type of MPN you have, you can go into more detail.

Don’t be afraid to ask your doctor or hematologist about the best way to explain complex medical terms to your loved ones. They can provide you with educational materials and explanations.

Talk With Others Who Understand

Find others to connect with at myMPNteam, the online social network for people and their loved ones living with myeloproliferative neoplasms. On myMPNteam, members come together to ask questions, give advice, and share their stories with others who understand life with MPNs.

Do you have more questions about MPNs or MDS? How do you explain your condition to others? Share your experience in the comments below, or start a conversation by posting on your Activities page.