TAL1 disruption at 1p32, a common rearrangement in the T-cell acute lymphoblastic leukemia, usually results in the formation of a SCL interrupting locus (SIL)-TAL1 fusion product. SIL is an immediate early gene whose expression is associated with cell proliferation. The Sil protein exhibits ubiquitous expression in hematopoietic cell lines and tissues. However, Sil protein levels remain tightly regulated during the cell cycle, achieving peak levels in mitosis and diminishing on transition to G1 phase. Overexpression of Sil in primary adenocarcinomas predicts metastatic spread, especially in lung tumors with increased mitotic activity.