A Unique Case of Concomitant T‐Prolymphocytic Leukemia and B‐Cell Acute Lymphoblastic Leukemia

T-prolymphocytic leukemia (T-PLL) is a rare lymphoid malignancy with a poor prognosis. B-cell acute lymphoblastic leukemia (B-ALL) also confers a poor prognosis, especially in patients with high-risk features without an option for transplant. Here, we present a case of a patient with T-PLL initially treated with multi-agent chemotherapy who then developed B-ALL, the management strategies, and possible pathogenesis of two concurrent rare malignancies. One proposed mechanism for the development of both hematologic malignancies in this patient is the acquisition of a <i>KMT2A</i> rearrangement, raising the possibility of clonal evolution resulting in therapy-related or secondary leukemia. Another explanation is the presence of a common clonal stem cell progenitor harboring a <i>JAK3</i> mutation.