['Chronic lymphocytic leukemia (CLL) is characterized by a clonal accumulation of neoplastic lymphocytes, indicating disruption of apoptosis.', 'Differential methylation hybridization analysis was performed to identify novel target genes silenced by CpG island methylation in patients with CLL.', 'Patched (PTCH), a tumor-suppressor gene, was found to be frequently methylated in CLL samples compared to samples derived from healthy individuals. De novo methylation of a CpG island region located upstream of PTCH exon 1 was confirmed by pyrosequencing in 17/37 (46%) of peripheral blood mononuclear cells of patients with CLL, but in none isolated from seven healthy individuals. No association was found between PTCH hypermethylation and currently used prognostic CLL factors.'] Does assessment of Promoter Methylation identify PTCH as a Putative Tumor-suppressor Gene in Human CLL?