Essential Thrombocythaemia

The goal of this clinical trial is to learn if the drug STP938 works to treat adults with high risk essential thrombocythaemia (ET) who are resistant to, or intolerant of, hydroxycarbamide (also known as hydroxyurea) therapy. The trial will also learn about the safety of STP938. The main questions the trial aims to answer are: * Does STP938 control platelet counts * Does STP938 control platelet counts without inducing unwanted side effects Participants will: * Take STP938 every day for up to 12 months. * Visit the clinic once every week for the first month, then every 2 weeks for checkups and tests. * Complete a questionnaire about symptoms once a month.

Philadelphia-negative myeloproliferative neoplasms (MPNs) occur sporadically and are due to somatic mutations in the JAK2 (Janus kinase 2), CALR (calreticulin) and MPL (thrombopoietin receptor) genes. However, data from epidemiological and family studies clearly highlight a heritable component that influences the risk of developing MPN and potentially contributes to the observed phenotypic pleiotropy. Genome-wide association studies in MPN familial clusters have identified a number of germline genetic variants associated with an increased risk of developing MPN. The strongest association discovered so far is the presence of the JAK2 46/1 haplotype and, subsequently, several studies have found additional variants in other genes, particularly in the TERT gene. The aim of the study would be to investigate the presence of germline mutations in MPN patients selected on the basis of a family history of myeloid neoplasms through the analysis of both already recognized genes and other potentially implicated ones.