Hydroxyurea in Chronic Myeloid Leukemia Management

Introduction to Hydroxyurea's Role

Hydroxyurea should be used only for a short time before initiating a tyrosine kinase inhibitor (TKI), until the diagnosis of CML has been confirmed, as stated by the European LeukemiaNet 1
The European LeukemiaNet explicitly states that busulfan is not recommended and hydroxyurea's role is limited to pre-TKI cytoreduction 1

Hydroxyurea is NOT recommended as definitive treatment for CML but serves only as a temporary cytoreductive agent before initiating TKI therapy, which should be started immediately upon BCR-ABL1 confirmation, according to the American Society of Hematology 1
Once BCR-ABL1 positivity is confirmed, TKI therapy should commence immediately, with hydroxyurea tapered before discontinuation, as recommended by the National Comprehensive Cancer Network 2

In adults, hydroxyurea (40 mg/kg body weight/day) may be used as initial therapy before confirmation of BCR-ABL1 fusion when there is immediate need for therapy due to high leukocyte counts or clinical symptoms, as suggested by the European Society for Medical Oncology 2
In pediatric patients, hydroxyurea (25-50 mg/kg/day in 2-3 divided doses) should be used in conjunction with intravenous hyperhydration for children with hyperleukocytosis (WBC >100 × 10⁹/L) and/or signs of leukostasis, according to the American Academy of Pediatrics 3, 4, 5

First-line treatment of chronic phase CML should be any of the three approved TKIs: imatinib (400 mg once daily), nilotinib (300 mg twice daily), or dasatinib (100 mg once daily), as recommended by the European LeukemiaNet 1
These TKIs target the molecular pathophysiology of CML and achieve deep molecular responses that translate to near-normal survival, which hydroxyurea cannot accomplish, according to the National Cancer Institute 1

The most critical error is continuing hydroxyurea beyond the brief period needed for diagnosis confirmation and initial cytoreduction, as warned by the American Society of Clinical Oncology 1, 2
Every day without TKI therapy represents lost opportunity for achieving optimal molecular responses that predict long-term survival, as emphasized by the European Society for Medical Oncology 1

If WBC >100 × 10⁹/L or symptomatic hyperleukocytosis: Start hydroxyurea 40 mg/kg/day (adults) or 25-50 mg/kg/day (pediatrics) with aggressive hydration (2.5-3 L/m²/day), as recommended by the International Society for Hematology 3, 4, 2, 5
Upon BCR-ABL1 confirmation, immediately initiate TKI therapy (imatinib, nilotinib, or dasatinib) and begin tapering hydroxyurea over 3-5 days, as suggested by the National Comprehensive Cancer Network 1, 2

The ELTS risk score should guide whether to use second-generation TKIs (nilotinib/dasatinib) upfront in high-risk pediatric patients, according to the European LeukemiaNet 5
Leukostasis is less common in children (16.5% incidence) despite higher median WBC counts (240,000/µL), but when present requires aggressive management, as recommended by the American Academy of Pediatrics 3, 4, 5

The National Comprehensive Cancer Network recommends immediate cytoreduction to prevent leukostasis complications, which can cause respiratory failure, neurological symptoms, and multiorgan dysfunction, in patients with extreme leukocytosis, such as a WBC count of 442.5 × 10⁹/L 6, 7
The National Comprehensive Cancer Network suggests that rasburicase should be considered as initial treatment if there is rapidly increasing blast counts, high uric acid levels, and evidence of impaired renal function 6, 7
Baseline CBC and comprehensive metabolic panel with uric acid and LDH should be obtained before initiating TKI therapy, as recommended by the National Comprehensive Cancer Network 6, 7
The National Comprehensive Cancer Network recommends continuing aggressive hydration and TLS prophylaxis until WBC count decreases and metabolic parameters stabilize 6, 7
Transfusion support, including RBC transfusions for symptomatic anemia and platelet transfusions for thrombocytopenic bleeding or platelet count <10,000/mm³, should be provided as needed, according to the National Comprehensive Cancer Network 6, 7
In transplant candidates, the National Comprehensive Cancer Network recommends using leukocyte-reduced blood products to prevent HLA alloimmunization and reduce CMV transmission risk 6, 7
CBC and comprehensive metabolic panel should be monitored every 2-4 weeks until doses are stabilized, then as clinically indicated, as recommended by the National Comprehensive Cancer Network 6, 7