Herein, we demonstrate the ability for MPseq to molecularly characterize 22 B-ALL/LBL specimens that were either positive for TCF3/PBX1 fusion or displayed an atypical TCF3 FISH pattern with additional or diminished TCF3 signals obtained by our TCF3/PBX1 D-FISH probe set. The gene discussed is PBX1; the disease is precursor B-cell acute lymphoblastic leukemia.