<b><i>JAK2</i></b>^V617F, <b><i>CALR</i></b>, and <b><i>MPL</i></b> Mutations and Bone Marrow Histology in Patients with Essential Thrombocythaemia

Mutations in the JAK2, CALR, and MPL genes have been shown to have prognostic value in essential thrombocythaemia (ET), but no clear association with morphological changes has been reported so far. We investigated the possible correlation between gene mutations and histopathological features in bone marrow (BM) biopsies of patients with ET. Methods: Marrow cellularity, fibrosis, and the number of total and dysmorphic megakaryocytes and clusters of megakaryocytes were compared to gene mutations in 90 cases of ET at diagnosis. Results: The JAK2V617F mutation was found in 58.9%, CALR in 28.9%, and MPL in 4.4% of the cases, and 7.8% were triple-negative. JAK2V617F-mutated ET showed a high BM cellularity, the lowest number of clusters of megakaryocytes and the highest number of dysmorphic megakaryocytes; CALR-mutated ET showed a reduced BM cellularity, many clusters of large megakaryocytes, and very few dysmorphic megakaryocytes; MPL-mutated ET showed the lowest BM cellularity, the highest number of clustered and large megakaryocytes, and the lowest number of dysmorphic megakaryocytes. Triple-negative ET cases had the highest BM cellularity. Conclusions: Distinct morphological patterns were associated with gene mutations in ET, supporting the classification of ET into different subtypes.