The Role of MicroRNAs in Hodgkin's Lymphoma

In this chapter, we summarize the current knowledge on microRNA (miRNA) expression, function and putative clinical value in Hodgkin's lymphoma (HL). HL is the second most common lymphoma subtype, and mainly affects young adults or elderly. Malignant cells in HL are scarce, usually less than 1%, and these cells are of B-cell origin. As miRNAs are involved in almost all known biological processes, deregulation of miRNAs is thought to play an important role in the pathogenesis of HL. MiRNA expression studies have been performed on HL cell lines, laser microdissected tumor cells, and total tumor tissue sections. Despite the use of different tissue specimens, a reasonable overlap has been found in the differentially expressed and highly abundant miRNAs. The most consistent highly expressed miRNAs include several known cancer-related miRNAs, for example, miR-16, miR-20a, miR-21, and miR-155. Functional studies on (deregulated) miRNAs in HL are performed for a limited number of miRNAs, but multiple functional target genes have been identified. Inhibition or overexpression of individual miRNAs in HL resulted in altered expression of target genes that are involved in apoptosis, proliferation, cytokine production, or plasma cell differentiation. In addition, low miR-135a levels in HL tumor cells are associated with low disease-free survival and high relapse rates. These miRNAs are potential novel therapeutic targets or prognostic markers. However, more studies are needed to identify possible clinical applications for miRNAs in HL.