Introduction
Mixed phenotype acute leukemia (MPAL), a rare type of acute leukemia that exhibits both myeloid and lymphoid features1, comprises 2%–4% of all acute leukemias, and approximately 87% of all MPALs are Philadelphia chromosome-negative.2 According to the 2016 World Health Organization (WHO) classification, Philadelphia chromosome-positive (Ph+) MPAL meets the diagnostic criteria for MPAL based on the presence of blasts harboring the t(9;22)(q34;q11) translocation or BCR-ABL1 rearrangement in the absence of a history of chronic myeloid leukemia (CML).3
There are currently no optimal treatments that have been established for Ph+ MPAL, which has a poor prognosis with a 2-year overall survival (OS) rate of 14%.4 Combination of the BCR-ABL inhibitor imatinib with chemotherapy has improved the 5-year OS rate to 54% in patients with Ph+ MPAL, which is comparable to that of patients with Ph+ acute lymphoblastic leukemia.5 Recent studies have reported higher efficacy with second-generation tyrosine kinase inhibitors (TKIs) compared to imatinib.6,7 However, optimal treatment approaches for elderly patients with Ph+ MPAL have not been established because of difficulties in the management of comorbidities in these patients. In elderly patients who cannot receive second-generation TKI therapy, imatinib can be considered as an alternative treatment option. However, the efficacy and optimal dose of imatinib in elderly patients with Ph+ MPAL are unknown.
Herein, we describe the case of an elderly patient with Ph+ MPAL who had a history of cardiovascular disease who was intolerant to dasatinib due to complications; however, switching to low-dose imatinib with monitoring of imatinib concentrations in blood achieved disease control and the continued safe use of imatinib.