# PT-1 (Primary Thrombocythaemia 1)

Source: https://onco.cc/trials/pt-1/  
OnCo record `pt-1` (Trial). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

PT-1 is the trial that made hydroxyurea the first-line drug in high-risk ET: anagrelide gave more arterial clots, more serious bleeding and more progression to myelofibrosis.

## Summary

PT-1 randomised 809 patients with high-risk essential thrombocythaemia to hydroxyurea or anagrelide, both with low-dose aspirin. After a median of 39 months the composite primary endpoint of arterial or venous thrombosis, serious haemorrhage or death from a thrombotic or haemorrhagic cause was more frequent on anagrelide (odds ratio 1.57); anagrelide gave more arterial clots, serious bleeding and transformation to myelofibrosis, and fewer venous clots (Harrison and colleagues, New England Journal of Medicine 2005). Registered as ISRCTN72251782.

## Fields

- Kind: Trial
- Status: positive
- Last checked: 2026-09-16
- Tags: essential-thrombocythaemia; mpn
- Phase: 3
- Setting: High-risk essential thrombocythaemia: hydroxyurea plus aspirin versus anagrelide plus aspirin
- Sponsor: Medical Research Council (UK)
- Enrolled: 809
- Result: Composite of thrombosis, serious haemorrhage or vascular death more frequent with anagrelide (odds ratio 1.57); more arterial clots, bleeding and myelofibrosis on anagrelide.

## Sources

- ISRCTN72251782: https://www.isrctn.com/ISRCTN72251782
- NEJM 2005: https://www.nejm.org/doi/full/10.1056/NEJMoa043800

## Connected records

- cancers: [Essential thrombocythaemia (ET)](https://onco.cc/cancers/essential-thrombocythaemia/), [Myeloproliferative neoplasms (PV, ET, myelofibrosis)](https://onco.cc/cancers/myeloproliferative-neoplasms/)
- drugs: [Anagrelide](https://onco.cc/drugs/anagrelide/), [Hydroxyurea (hydroxycarbamide)](https://onco.cc/drugs/hydroxyurea/)

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JSON: https://onco.cc/api/v1/entities/pt-1.json