Genetic amplification at chromosome 8p23.1 has been reported in some solid tumors. Translocation of 8p23.1 has also been reported in hematological malignancies and head and neck squamous cell cancer. In an attempt to clarify whether this translocation is implicated in lymphomagenesis, we performed FISH analysis of the immunoblastic B-cell lymphoma cell line OCI-LY8, which has chromosome translocation at 8p23.1, with various BAC clones. We found split signals on BAC, RP11-18L2 where the MASL1 gene is located. This translocation was found to produce a chimeric transcript of MASL1 exon 1 with a cryptic exon from the genome region at 14q21. Our study indicates that MASL1 is not only a target gene for genomic amplification but also for chromosomal translocation. Since tumorigenic activity of the MASL1 has not been proven, its in vitro transforming activity was studied and in vivo nude mice assay were performed. Although no in vitro transforming activity was detected by focus formation, the in vivo tumorigenesis assay with nude mice showed that both MASL1 and chimeric MASL1 possess tumorigenic activity. This suggests that MASL1 is an important oncogene not only for solid tumors but also for hematologic malignancies.