PCDH10has been implicated as a tumor suppressor, since epigenetic alterations of this gene have been noted in multiple tumor types. However, to date, studies regarding its role in acute and chronic leukemias are lacking. Here, we have investigated the presence of promoter hypermethylation of two CpG islands of thePCDH10gene by methylation-specific PCR in 215 cases of various subsets of myeloid- and lymphoid-lineage leukemias. We found thatPCDH10promoter hypermethylation was frequent in both B-cell (81.9%) and T-cell (80%) acute lymphoblastic leukemia (ALL), while it was present in low frequency in most subtypes of myeloid leukemias (25.9%) and rare in chronic myeloid leukemia (2.2%).PCDH10expression was downregulated via promoter hypermethylation in primary ALL samples (N= 4) and leukemia cell lines (N= 11). The transcriptional repression caused byPCDH10methylation could be restored by pharmacologic inhibition of DNA methyltransferases. ALL cell lines harboring methylation-mediated inactivation ofPCDH10were less sensitive to commonly used leukemia-specific drugs suggesting thatPCDH10methylation might serve as a biomarker of chemotherapy response. Our results demonstrate thatPCDH10is a target of epigenetic silencing in ALL, a phenomenon that may impact lymphoid-lineage leukemogenesis, serve as an indicator of drug resistance and may also have potential implications for targeted epigenetic therapy. © 2011 Wiley Periodicals, Inc.