CD99 and prostate cancer: In other tumors, such as Hodgkin lymphoma (Kim et al. 2000), OS (Manara et al. 2006; Scotlandi et al. 2007), prostate cancer and gastric cancer (Jung et al. 2002; Scotlandi et al. 2007), CD99 is expressed at low levels and the downregulation of CD99 rather than its over-expression seems to be required for tumorigenesis.