Histological evaluation of myeloproliferative neoplasms

Cytological Diagnosis of Classic Myeloproliferative Neoplasms at the Age of Molecular Biology

Myeloproliferative neoplasms (MPN) are clonal hematopoietic stem cell-derived disorders characterized by uncontrolled proliferation of differentiated myeloid cells. Two main groups of MPN, BCR::ABL1-positive (Chronic Myeloid Leukemia) and BCR::ABL1-negative (Polycythemia Vera, Essential Thrombocytosis, Primary Myelofibrosis) are distinguished. For many years, cytomorphologic and histologic features were the only proof of MPN and attempted to distinguish the different entities of the subgroup BCR::ABL1-negative MPN. World Health Organization (WHO) classification of myeloid neoplasms evolves over the years and increasingly considers molecular abnormalities to prove the clonal hematopoiesis. In addition to morphological clues, the detection of JAK2, MPL and CALR mutations are considered driver events belonging to the major diagnostic criteria of BCR::ABL1-negative MPN. This highlights the preponderant place of molecular features in the MPN diagnosis. Moreover, the advent of next-generation sequencing (NGS) allowed the identification of additional somatic mutations involved in clonal hematopoiesis and playing a role in the prognosis of MPN. Nowadays, careful cytomorphology and molecular biology are inseparable and complementary to provide a specific diagnosis and to permit the best follow-up of these diseases.

Essential Thrombocythemia and Post-Essential Thrombocythemia Myelofibrosis: Updates on Diagnosis, Clinical Aspects, and Management

Although several decades have passed since the description of myeloproliferative neoplasms (MPN), many aspects of their pathophysiology have not been elucidated. In this review, we discuss the mutational landscape of patients with essential thrombocythemia (ET), prognostic scores and salient pathology, and clinical points. We discuss also the diagnostic challenges of differentiating ET from prefibrotic MF. We then focus on post-essential thrombocythemia myelofibrosis (post-ET MF), a rare subset of MPN that is usually studied in conjunction with post-polycythemia vera MF. The transition of ET to post-ET MF is not well studied on a molecular level, and we present available data. Patients with secondary MF could benefit from allogenic hematopoietic stem cell transplantation, and we present available data focusing on post-ET MF.

Myeloproliferative neoplasms: Diagnostic workup of the cythemic patient

Elevated peripheral blood (PB) cell counts, such as leukocytosis, thrombocytosis, and polycythemia, are often the presenting symptom in patients with myeloproliferative neoplasms (MPN). Because cythemias are nonspecific and may reflect either a reactive or neoplastic process, diagnostic workup of these patients is complicated and requires integration of numerous diagnostic modalities. Careful morphologic evaluation of the PB smear may provide insights into the underlying cause of the abnormal counts (such as the presence of teardrop erythrocytes in myelofibrosis or granulocytic dysplasia with left shift in atypical chronic myeloid leukemia). However, these morphologic findings need to be interpreted in concert with clinical findings and other laboratory results. In recent years, there has been a wealth of new genetic data in the field of MPN and many recurrent mutations have been identified, especially in cases lacking Philadelphia chromosome. Many of these genes impact the diagnosis and/or prognosis. Although certain mutations are preferentially enriched in specific MPN types, none of these mutations are disease defining; therefore, a thorough workup should always include a bone marrow biopsy for morphologic evaluation and diagnosis. This review will describe a comprehensive approach to the diagnosis of various MPN, with an emphasis on the diagnostic and prognostic implications of recurrent mutations in MPN.