Prevalence and Real-World Clinical Outcomes of Hydroxyurea Resistance and Intolerance in Polycythemia Vera and Essential Thrombocythemia: A Single-Centre Experience.

The clonal myeloid stem cell disorders, polycythemia Vera (PV) and essential Thrombocythemia (ET) are classified as Philadelphia chromosome negative myeloproliferative neoplasms (MPNs). The present study was done to evaluate the clinical response and survival outcomes of Hydroxycarbamide (HC) intolerance and resistance in adult PV and ET patients. A retrospective cohort study recruiting 81 patients was conducted at National Institute of Blood Diseases and Bone Marrow Transplantation (NIBD & BMT) from June 2012 to December 2024, and included patients of PV and ET who were treated with Hydroxycarbamide (HC) from 500 mg/day up to 3000 mg/day. Conventional risk stratification and European Leukemia Net (ELN) risk stratification criteria were implemented for PV and ET, respectively. Moreover, HC resistance or intolerance was evaluated using modified ELN (mELN) criteria. Out of 81 patients, 42 PV (51.9%) and 39 ET (48.1%) were evaluated. Higher median age was observed in PV as compared to ET (54.5 vs. 40 years). Consequently, risk stratification classified 33.3% of PV and 23.1% of ET patients to be high-risk. However, 23.0% and 4.3% of PV and ET patients with HC resistance transformed to myelofibrosis respectively. The prevalence of HC resistance was 30.9% in PV and 58.9% in ET, whereas HC intolerance was observed to be 26.1% in PV and 15.3% in ET. The patient's health improved significantly, as evident by a decline in active disease symptoms from 88.2% at baseline to 17.9% at 12 months.