Myeloproliferative neoplasms are a group of rare disorders of the bone marrow. Find out what they are and the different types.

What it is

Myeloproliferative neoplasms are a group of rare disorders of the bone marrow that cause an increase in the number of blood cells. You may also hear doctors call them MPN or myeloproliferative disorders (MPD).

Myeloproliferative neoplasm is a term that doctors use both for cancers (malignant neoplasms) and non cancerous tumours (benign neoplasms). There is some debate about whether these conditions should be regarded as cancers or not.

These conditions are rare and usually develop slowly over a number of years. Most people diagnosed are over 60. Many have other health problems which can make treatment more difficult. The aim of treatment is usually to control symptoms rather than cure the condition.

The bone marrow and blood cells

Different myeloproliferative disorders affect different blood cells that form in the bone marrow. The bone marrow is the soft inner part of our bones that makes the blood cells.

All blood cells start from the same type of cell called a stem cell. The stem cell makes immature blood cells. These immature cells go through various stages of development before they become fully developed blood cells and are released into the blood as:

• red blood cells to carry oxygen around the body
• white blood cells to fight infection
• platelets to help the blood clot

The diagram shows how the various different types of cells develop from a single blood stem cell.

Which type of myeloproliferative disorder you have relates to:

• the type of blood cells affected
• the number of blood cells in your bloodstream
• your symptoms
• the treatment you will have

Types of myeloproliferative disorders

There are a number of different types of myeloproliferative disorders. We have separate information on these types:

The following types are rarer:

• chronic neutrophilic leukaemia – a rare type of leukaemia affecting neutrophils, a type of white blood cell which help us fight bacterial and viral infections
• chronic eosinophilic leukaemia – affects the eosinophils, a white blood cell which is involved in allergic reactions and used to fight parasites
• mastocytosis – is when you have too many mast cells which help protect us from infections in particular tissues such as the skin, lungs and bowel

There are also very rare disorders that do not fall into any of the groups above and that the World Health Organisation group together as 'MPN which is not classified'.