Abstract
Lineage switch in acute leukemias is a well-reported occurrence; however, most of these cases involve a switch from either lymphoid to myeloid or myeloid to lymphoid lineage. Here, we report a case of a 14-year-old male with B-cell acute lymphoblastic leukemia (B-ALL) who initially responded well to standard chemotherapy but then later developed mixed phenotype acute leukemia (MPAL) at relapse, likely reflecting a clonal evolution of the original leukemia with a partial phenotypic shift. The patient had a del(9)(p13p21) in his leukemia blasts at diagnosis, and the deletion persisted at relapse along with multiple additional cytogenetic aberrations. Interestingly, the patient presented with an isolated testicular lesion at relapse, which on further analysis revealed both a lymphoid and myeloid component. Unfortunately, the patient did not respond well to treatment at relapse and eventually succumbed to his disease. To our knowledge, an isolated extramedullary MPAL at relapse in a patient with previously diagnosed B-ALL has not been reported in the literature before.
Highlights
Mixed phenotype acute leukemia (MPAL) is a rare but well-described form of childhood leukemia, with the leukemic blasts expressing features of both lymphoid and myeloid lineage [1,2,3,4,5]
Isolated extramedullary MPAL at relapse in a previously diagnosed B-cell acute lymphoblastic leukemia (B-ALL) case is to our knowledge entirely undocumented in the literature
The case describes a unique presentation of clonal evolution of B-ALL to MPAL, MPAL
Summary
Mixed phenotype acute leukemia (MPAL) is a rare but well-described form of childhood leukemia, with the leukemic blasts expressing features of both lymphoid and myeloid lineage [1,2,3,4,5]. These cases typically have a de novo presentation, with the initiating cell believed to be an early common lineage precursor cell. Lineage switch in acute leukemias is a well-reported phenomenon, believed to be related to the plasticity of the initiating leukemia stem cell [6] Most of these cases involve a switch from either lymphoid to myeloid or myeloid to lymphoid lineage [6]. Persistently harboring the del(9)(p13p21) with additional cytogenetic aberrations
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