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Background: Besides essential thrombocythemia (ET), polycythemia vera (PV) and primary myelofibrosis (PMF) the myeloproliferative neoplasms (MPN) defined by the World Health Organization (WHO) comprise the entity of unclassifiable MPNs (MPN, U). The exact differential diagnosis of the specific MPN entities can be challenging particularly at early stages of the diseases. So far, pathologists have had to rely only on histomorphological evaluation of bone marrow biopsies in combination with laboratory data because helpful ancillary tests are not yet available. Even molecular tests, such as JAK2 mutation analysis are not helpful particularly in the differential diagnosis of ET and PMF because both entities are associated with the V617F mutation in 50 % of the cases. Recently overexpression of the transcription factor NF-E2 in MPN was described., Materials and Methods: A collective of samples consisting of 163 bone marrow biopsies including 139 MPN cases was stained immunohistochemically for NF-E2 and analyzed regarding the subcellular localization of NF-E2 in erythroid progenitor cells. The results were compared between the MPN entities as well as the controls and statistical analyses were conducted., Results and Discussion: This study showed that NF-E2 immunohistochemistry and analysis of the proportion of nuclear positive erythroblasts of all erythroid precursor cells can help to distinguish between ET and PMF even in early stages of the diseases. An MPN, U case showing a proportion of more than 20 % nuclear positive erythroblasts can be classified as a PMF with 92 % accuracy.

Bone marrow diagnostics is an essential tool in routine hematological clinical practice. Not only conventional cytological and histological approaches but also more modern techniques, such as immunohistochemistry, cytogenetics and molecular diagnostics are used. The molecular basis of more and more hematological disorders is being discovered and makes its way not only into routine diagnostics but also into daily clinical practice. Recurrent genomic aberrations associated with the individual patient prognosis are well characterized and are being applied in differential therapeutic decisions. In addition, understanding deregulated biochemical pathways have led to the development of targeted therapeutic approaches. This review outlines the value of bone marrow diagnostics in hematological diseases with a focus on the currently emerging molecular diagnostic possibilities.