What are Chronic Myeloproliferative Diseases?

Chronic myeloproliferative diseases are cancers or other disorders that begin in the bone marrow and result in an over-production of certain blood cells. In medicine, at least in this context, the prefix myelo- refers to the bone marrow.

The bone marrow creates blood stem cells. These blood stem cells develop into either a myeloid stem cell or a lymphoid stem cell. Myeloid stem cells can develop into:

• - Red blood cells
• - White blood cells
• - Platelets

In the case of myeloproliferative cancers, instead of these myeloid stem cells developing equally into one of the three possible cells, too many of them develop into one of the three possible cells. The type of myeloproliferative disease is dictated by which blood cell is being over-produced.

WHO Classification

The World Health Organization features seven diseases in its classification of chronic myeloproliferative diseases (each disease is followed by the type of blood cell affected):

• - Chronic myelogenous leukemia, BCR/ABL-positive (non-lymphocyte white blood cells)
• - Chronic neutrophilic leukemia (neutrophils, a white blood cell)
• - Chronic eosinophilic leukemia (eosinophils, a white blood cell)
• - Polycythemia vera (red blood cells)
• - Chronic idiopathic myelofibrosis
• - Essential thrombocythemia (thrombocyte is another word for platelet)
• - Chronic myeloproliferative disease, unclassifiable

That last one, in similar iterations, appears on most lists like this, attempting a catch-all category for the many case studies and other instances when people develop diseases organically and they just don't allow themselves to be pigeon-holed. The further we get into sequencing entire cancer genomes, the more jumbled that last category becomes, and the longer these lists become.

In chronic myeloproliferative diseases too, while one blood cell is affected by overproduction more than the others, the others may be overproduced as well.

Staging

Chronic myeloproliferative diseases are not given stages to designate how far they have spread because the disease doesn't present that way. Further, myeloid cancers in general, by definition, are only classified by whether they are in the chronic phase or the acute phase.

The JAK2 gene

Using cytogenetic and genomic analysis, scientists can look for a specific mutation in the JAK2 gene, which is commonly found in patients with essential thrombocythemia, myelofibrosis, and polycythemia vera.

Sources:
The WHO classification of the myeloid neoplasms
National Cancer Institute