Imatinib-induced severe hematological toxicity: Prolonged myelosuppression resulting from extraordinary sensitivity in an old age

The advent of tyrosine kinase inhibitors (TKIs) has profoundly changed the therapeutic landscape of chronic myeloid leukemia (CML) in the chronic phase (CML-CP). Imatinib is the first-generation, and the first and as yet the most widely used TKI, and the recommended dose is 400 mg/day for treating CML-CP. Most patients tolerate this treatment well, and prolonged hematological toxicities have rarely been reported. In this manuscript, we report a newly diagnosed CML-CP patient who developed prolonged myelosuppression (lasting for more than three months) following only one week of imatinib at 400 mg/day as the solitary treatment. Imatinib was discontinued, and pancytopenia persisted, with a continuous decrease in hemoglobulin levels. After restoration of autologous hematopoiesis, reintroduction of imatinib at 100 mg/day resulted in recurrent myelosuppression, and subsequent treatment with imatinib at 50 mg/day achieved good hematological homeostasis. We hypothesized that extraordinary sensitivity resulted in severe and prolonged myelosuppression.

A Case of Tyrosine Kinase Inhibitor-Induced Bone Marrow Aplasia That Was Successfully Treated with Allogeneic Hematopoietic Stem Cell Transplantation

Here, we present a rare case of tyrosine kinase inhibitor (TKI)-induced bone marrow aplasia. A 58-year-old man presented with leukocytosis and was diagnosed with chronic myeloid leukemia. He was initially treated with imatinib for 6 years and abruptly discontinued treatment by himself. He was administered dasatinib 5 years after treatment interruption, and presented with pancytopenia 6 months after dasatinib initiation. Bone marrow biopsy revealed severe hypocellularity without blasts. Dasatinib was discontinued, and he recovered from pancytopenia 3 months later; however, BCR-ABL1 was positive for almost all white blood cells in the peripheral blood. We retreated with ponatinib, but pancytopenia developed again. The clinical course indicated TKI-induced bone marrow aplasia. Therefore, ponatinib was discontinued and the patient received an allogeneic hematopoietic stem cell transplantation from a haploidentical daughter using post-transplant cyclophosphamide. He had a major molecular response and had normal complete blood counts and bone marrow 1 year after transplantation.

Unexpected pancytopenia: Dasatinib induced aplastic anemia in chronic myeloid leukemia

INTRODUCTION

The use of TKIs in CML has dramatically altered the natural course of the disease and improved outcomes for patients. TKIs overall have a very favorable safety profile. Dasatinib, a second generation TKI, is commonly used as a first-line treatment option in CML.

CASE REPORT

We describe the first two reported cases of first-line dasatinib induced aplastic anemia in CML. In both patients, pancytopenia occurred within one year of diagnosis/starting dasatinib. Both bone marrow biopsies showed hypocellularity with mild fibrosis and persistent BCR-Abl1 positivity.

MANAGEMENT & OUTCOME

Dose reduction was attempted without success in both patients. In one patient, multiple TKIs were trialed, while in the other, growth factor support was attempted; neither regimen was effective. Ultimately, the cytopenias associated with dasatinib were only resolved after immunosuppression in one patient and allogeneic stem cell transplant in the other patient.

DISCUSSION

Prior reports have shown that aplasia/aplastic anemia can rarely be associated with imatinib and nilotinib. Here we show that dasatinib can lead to this phenomenon as well. This diagnosis should be considered in patients with CML who unexpectedly develop cytopenias.

Aplasia in Chronic Phase CML Post-TKI Therapy: A Management Dilemma

Transient cytopenias and bone marrow hypoplasia commonly occur during treatment of CML with TKIs (tyrosine kinase inhibitors). This is usually related to the eradication of CML clones that initially compose the majority of hematopoietic cells in the bone marrow at the time of diagnosis. With continuation of effective therapy, normal blood counts return as normal hematopoiesis is restored and CML clones are reduced. Though rare and more unusual than myelodysplastic syndrome (MDS), isolated instances of persistent marrow aplasia have been documented with chronic use of TKIs. We describe two such instances of chronic phase CML where no significant reduction of CML clones was achieved following treatment with TKIs, but bone marrow aplasia occurred resulting in persistent dysfunctional hematopoiesis. Due to prolonged aplasia/hypoplasia, such patients are no longer amenable to TKI treatment. CML progression to accelerated or blast phase in that setting would likely be fatal.

Hematologic toxicities of small molecule tyrosine kinase inhibitors

Small molecule tyrosine kinase inhibitors (TKIs) are potent anti-cancer targeted therapies. TKIs are considered safe and efficacious therapeutic modalities, and are generally tolerated well. However, they are associated with certain side effects including hematologic toxicities such as anemia, macrocytosis, neutropenia, thrombocytopenia, hemolytic anemia, bone marrow aplasia and necrosis. Thrombotic microangiopathy, arterial thromboembolism and splenic infarction can also occur following treatment with TKIs. Cytopenias are the most common adverse effects associated with these agents, and other hematologic toxicities are not frequent. It is essential for clinicians to monitor patients closely, and recognize those side effects as early as possible, in order to improve efficacy of small molecule TKIs and optimize outcomes. This article summarizes hematologic toxicities associated with the commonly used small molecule TKIs. It also provides practical strategies for the management of these toxicities.