A large series of drugs, e.g., histone deacetylase inhibitors (HDACi), histone methyl-transferase inhibitors (HMTi), and DNA metyl-transferase inhibitors (DNMTi) are suggested that their anti-tumor activity is at least partially mediated by targeting abnormal epigenetic patterns in tumor tissue inhibiting tumor cell differentiation. This evidence concerns the gene PRDM9 and neoplasm.