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.
Adults aged 18 years or older
A confirmed diagnosis of ET according to World Health Organisation (WHO) or British Society for Haematology (BSH) criteria.
Meeting criteria for high risk ET.
Raised platelet count (>600 x109/L) requiring cytoreductive therapy.
Subjects currently or recently receiving cytoreductive therapy for the treatment of essential thrombocythaemia (wash out periods apply).
Subjects who have received any investigational agents for the treatment of essential thrombocythaemia within 4 weeks before enrolment or less than 5 half-lives since completion of prior therapy, whichever is shorter.
Proven or suspected transformation to polycythaemia vera, myelofibrosis, myelodysplasia, acute myeloid leukaemia or another myeloid neoplasm.
Known malabsorption syndrome or other condition that may impair absorption of study medication (e.g. gastrectomy).