In myeloproliferative neoplasms (myelo = bone marrow; proliferative = rapid multiplication; and neoplasm = new abnormal growth, such as a precancer or cancer), the blood-producing cells Formation of Blood Cells Red blood cells, most white blood cells, and platelets are produced in the bone marrow, the soft fatty tissue inside bone cavities. Two types of white blood cells, T and B cells ( lymphocytes)... read more in the bone marrow (precursor cells, also called stem cells) develop and reproduce excessively or are crowded out by an overgrowth of fibrous tissue. Sometimes, blood-producing cells appear and reproduce in the spleen and liver. Myeloproliferative neoplasms are caused by genetic mutations. Typically the mutations are acquired and not inherited, although rarely there are families in which several members have these disorders.
The myeloproliferative neoplasms include
In most people, a myeloproliferative neoplasm progresses or transforms to acute leukemia Overview of Leukemia Leukemias are cancers of white blood cells or of cells that develop into white blood cells. White blood cells develop from stem cells in the bone marrow. Sometimes the development goes awry... read more .
Less common myeloproliferative neoplasms include hypereosinophilic syndromes Hypereosinophilic syndrome Eosinophils are a type of white blood cell that play an important role in the body's response to allergic reactions, asthma, and infection with parasites. These cells have a role in the protective... read more 
and chronic neutrophilic leukemia. There are also rare myeloproliferative neoplasms that overlap with myelodysplastic syndrome Myelodysplastic Syndrome (MDS) Myelodysplastic syndrome refers to a group of related disorders in which abnormal blood-forming cells develop in the bone marrow. At first, these cells interfere with the production of normal... read more , another type of condition with abnormal blood-forming cells in the bone marrow.
Each myeloproliferative neoplasm is identified according to its predominant bone marrow and blood characteristics. Each disorder has a somewhat typical set of examination findings, test results, and expected course; however, there may be some overlap of features among these disorders because they share the same genetic mutations.
The number of blood-producing cells in the bone marrow can also increase as a reaction to another underlying disorder. For example, lack of oxygen can cause the red blood cells to increase, a serious infection can cause the white blood cells to increase, and inflammation can cause the platelets to increase. In these cases, an increased number of cells in the bone marrow is not considered a myeloproliferative neoplasm but rather a benign reaction. Treating the underlying disorder restores the number of blood cells being produced to normal.
