A novel cell line, SACHI, was established from a pericardial effusion developed during the course of primary plasma cell leukemia (PCL). The cell line SACHI cells were the same as the infiltrating plasma cells with regard to surface markers (CD38(+)CD19(-)PCA-1(+)VLA-5(-)CD56(-)TdT(+)) and immunoglobulin gene rearrangements. Analysis of SACHI cells showed a complex hypertriploid (karyotype mode 70-73) including 7p32, 14q32, and Xq24 structural abnormalities, which were found also in the original leukemia cells. Dual-color fluorescence in situ hybridization revealed that the c-MYC gene was juxtaposed with a constant region of IgG (Cgamma) on 14q32. The split Cgamma locus was fused near the MAFB gene on chromosome 20. The SACHI cells had increased amounts of c-MYC and MAFB transcripts. Injection of SACHI cells into NOD/SCID mice generated leukemic plasmacytosis with invasion to liver, spleen, and bone marrow. This cell line may be useful for therapeutic testing as well as analyzing the molecular pathogenesis of PCL.