Zarzour, Ahmad

Tyrosine kinase inhibitors (TKI) are the initial treatment for majority of newly diagnosed patients with chronic myelogenous leukemia (CML) in chronic phase (CP) and are associated with marked improvement in hematological, cytogenetic, molecular response and survival rates compared with other therapies. In this review, we summarize the evidence of TKI efficacy for patients with newly diagnosed CP‐CML. Six trials at low risk of bias evaluating TKIs as an initial treatment in adults with newly diagnosed CP‐CML and enrolling 2,456 patients were included. Follow‐up times ranged from a median of 3 months to 5 years. Direct comparison showed statistically higher rates of major molecular response (MMR ≤ 0.1%IS) achievement with second‐generation TKIs at 12 months which was sustained throughout treatment period. Bayesian mixed‐treatment comparison (MTC) analysis demonstrated superiority of both nilotinib and dasatinib over imatinib in terms of efficacy. Nilotinib was associated with higher deeper molecular responses (MR4.5 ≤ 0.0032%IS) at 60 months than dasatinib but no difference in MMR. The differences between nilotinib and dasatinib are likely clinically trivial. Among TKIs, nilotinib was found to have the best survival profile. Both nilotinib and dasatinib are associated with significantly better MMR compared to imatinib that is sustained over 60 months. This analysis shows that new‐generation TKIs are not only showing faster response but also maintaining a more potent one through longer follow‐up period. It is important to note out that MTC is not a substitute for well‐conducted RCTs investigating direct comparisons.

Myeloproliferative neoplasms (MPNs) are clonal hematopoietic stem-cell disorders, characterized phenotypically by the abnormal accumulation of mature-appearing myeloid cells. Polycythemia vera, essential thrombocythemia, primary myelofibrosis (also known as ‘ BCR-ABL1-negative’ MPNs), and chronic myeloid leukemia (CML) are the primary types of MPNs. After the discovery of the BCR-ABL1 fusion protein in CML, several oncogenic tyrosine kinases have been identified in ‘ BCR-ABL1-negative’ MPNs, most importantly, JAK2V617F mutation. The similarity in the clinical characteristics of the BCR-ABL1-negative MPN patients along with the prevalence of the Janus kinase mutation in this patient population provided a strong rationale for the development of a new class of pharmacologic inhibitors that target this pathway. The first of its class, ruxolitinib, has now been approved by the food and drug administration (FDA) for the management of patients with intermediate- to high-risk myelofibrosis. Ruxolitinib provides significant and sustained improvements in spleen related and constitutional symptoms secondary to the disease. Although noncurative, ruxolitinib represents a milestone in the treatment of myelofibrosis patients. Other types of JAK2 inhibitors are being tested in various clinical trials at this point and may provide better efficacy data and safety profile than its predecessor. In this article, we comprehensively reviewed and summarized the available preclinical and clinical trials pertaining to JAK inhibitors.