CD99 and neoplasm: However, there is an emerging group of neoplasms, including pancreatic endocrine neoplasms, gastric adenocarcinoma (Jung et al. 2002; Maitra et al. 2003) and osteosarcoma (OS) (Manara et al. 2006), in which CD99 expression is diffuse in benign diseases and absent in the malignant counterparts.