Thy-1 or CD90 (Cluster of Differentiation 90) is a 25 - 37 kDa heavily N-glycosylated, glycophosphatidylinositol (GPI) anchored conserved cell surface protein with a single V-like immunoglobulin domain originally discovered as a thymocyte antigen. CD90 is expressed on thymocytes, neurons, glial cells, endothelial cells, fibroblasts, fetal liver cells and haematopoietic stem cells in normal bone marrow and cord blood. Thy-1 has been used as a marker for a variety of stem cells and for the axonal processes of mature neurons. CD90 is associated with unfavorable clinical and biological features in acute myeloid leukemia. In prostate cancer, CD90 has been reported to be overexpressed in cancer associated fibroblasts and serve as a marker for prostate cancer-associated stroma.