Case of B-acute lymphoblastic leukaemia with t(1;19)(q23;p13.3) <i>TCF3::PBX1</i> and co-occurring <i>CBL</i> mutation in an elderly patient

The t(1;19) (q23;p13) <i>TCF3::PBX1</i> is a well-described, recurring chromosomal abnormality in B-acute lymphoblastic leukaemia (B-ALL) that has historically been associated with a worse prognosis in paediatric patients. Gene expression profiling has demonstrated that <i>TCF3::PBX1</i> results in a distinct subtype of B-ALL, leading to its recognition in the most recent WHO and ICC classifications. Though initially believed to be a poor prognostic sign in the adult population, emerging evidence suggests its presence may instead be intermediate or even favourable in B-ALL. However, adults with <i>TCF3::PBX1</i> are typically younger and often qualify for treatment with paediatric-inspired regimens. Thus, the prognostic significance in this population remains unclear. This translocation appears to be very rare in older adults with B-ALL and its predictive and prognostic nature in this population is unknown. Herein, we explore a case of this translocation occurring in a patient in her 70s. She initially presented to the emergency department with abdominal pain and thrombocytopenia and was subsequently diagnosed with B-ALL. In addition to t(1;19) (q23;p13), a pathologic mutation in the <i>CBL</i> gene was identified. <i>CBL</i> mutations have been implicated in cancer progression and are mostly described in paediatric B<b>-</b>ALL. She was treated with modified Ph-negative EWALL induction (Vincristine, Idarubicin, dexamethasone) and achieved a complete remission. However, she subsequently experienced an early relapse and was refractory to targeted therapy with blinatumomab. After treatment with inotuzumab ozogamicin, she achieved a second complete remission. Unfortunately, she then suffered a central nervous system (CNS) relapse and passed away from complications of her disease. This case serves as an example of the heterogeneous nature of B-ALL. It demonstrates that patients with ostensibly favourable prognostic factors may experience poor response rates to traditional chemotherapy as well as targeted salvage agents. It also illustrates the challenges of treating B-ALL in the elderly population.