Tumorigenesis is a multistep process controlled by a number of proteins involved in diverse pathways. Traditionally, proteins are either considered as oncogenes, which promote tumorigenesis or as tumor suppressors, which prevent tumorigenesis. However, recent studies revealed quite a few proteins that could function as oncogene as well as tumor suppressor. A new member of such proteins is p30 DBC (deleted in breast cancer 1, also called DBC1). p30 DBC is one of the proteins involved in tumorigenesis that does not clearly adhere to either descriptions. Several studies show that p30 DBC is involved in cell proliferation, apoptosis and histone modification, all processes important for regulating tumorigenesis. However, there are other conflicting results regarding how p30 DBC contributes to tumorigenesis. The most interesting aspect of this is that p30 DBC is a strong inhibitor of SIRT1 protein deacetylase, whose exact role in tumorigenesis is currently under debate. This review summarizes the current understandings on p30 DBC functions, with a focus on the proposed roles of p30 DBC in tumorigenesis.