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

## TL;DR

This paper describes a rare case where a patient developed two types of leukemia, T-PLL and B-ALL, and explores possible reasons for their co-occurrence.

## Contribution

The novelty lies in presenting a unique case of concurrent T-PLL and B-ALL and proposing potential mechanisms for their development.

## Key findings

- The patient initially diagnosed with T-PLL later developed B-ALL.
- A KMT2A rearrangement may explain the development of both leukemias.
- A JAK3 mutation in a common stem cell progenitor is another possible explanation.

## Abstract

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 KMT2A 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 JAK3 mutation.