B cell lymphoma-6 (BCL6) is a transcriptional repressor that recruits Hdac3 to repress the transcription of DNA damage response genes such as ATM and ATR that signal to the p53 tumor suppressor. BCL6 is the target of chromosomal translocations in diffuse large B cell lymphoma, which drive high, continuous, levels of BCL6 to suppress p53 functions and drive lymphoma development. As a key enzyme that mediates BCL6 functions, Hdac3 is an attractive therapeutic target in the diffuse large B cell lymphoma and other cancers that over express BCL6 (up to 30% of DLBCL). Our preliminary data suggests that deletion of Hdac3 in B cells causes a phenotype similar to that observed upon inactivation of Bcl6. Moreover, diffuse large B cell lymphoma cell lines that are dependent on BCL6 were sensitive to Hdac3-selective inhibitors. As such, we hypothesize that inhibition of Hdac3 will prevent or cure B cell lymphoma driven by BCL6 over- expression.