Overview of myeloproliferative neoplasms

[Tariq Zaki]

In myeloproliferative neoplasms (myelo = bone marrow; proliferative = rapid multiplication; and neoplasm = new abnormal growth), the blood-producing cells 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

Polycythemia vera
Primary myelofibrosis
Essential (primary) thrombocythemia
Chronic myeloid leukemia

In a small number of people, the myeloproliferative neoplasm progresses or transforms to acute leukemia.
Less common myeloproliferative neoplasms include the hypereosinophilic syndromes and chronic neutrophilic leukemia. There are also rare myeloproliferative neoplasms that overlap with myelodysplastic syndrome.
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.