Protein kinase D3 (PRKD3) belongs to the multigene protein kinase D family of serine/threonine kinases, which has been implicated to regulate cancer progression in a broad range of cancer types.[19, 20] Our groups have identified PRKD3 as a breast cancer susceptibility gene using transposon insertional mutagenesis in mice, implicating a potential important oncogenic role of PRKD3 in breast cancer.[21] In this study, we define PRKD3 to be a key regulator of CLU. This evidence concerns the gene MARK2 and breast cancer.