Extramedullary breast infiltration as the initial manifestation of adult acute B-lymphoblastic leukemia with TCF3::PBX1 fusion gene recurrence and adenofibroma: A case report.

Extramedullary breast relapse of leukemia is uncommon and primarily occurs in cases of acute myeloid leukemia(AML), and secondary acute lymphoblastic leukemia (ALL) affecting the breast may also occur occasionally. The mechanism of extramedullary involvement remains unclear; patients' risk of hematological recurrence is high. TCF3::PBX1 (also known as E2A:: PBX1) is an oncogenic transcription factor arising from the T (1; 19) (q23; P13) translocation, observed in 5 % to 6 % of childhood acute lymphoblastic leukemia (ALL) cases and approximately 3 % of adult ALL cases. Here, we report a case of B-ALL with TCF3::PBX1 fusion gene, where extramedullary breast infiltration was the earliest clinical indication of recurrence. Adult ALL with the TCF3::PBX1 fusion gene is relatively uncommon compared to other ALL. Despite the satisfactory effect of chemotherapy, the patient ultimately decided to discontinue treatment following breast infiltration by ALL.