THY1 and cancer: Possible reasons for the high rates of recurrence after surgery include primary cancer cell dissemination, the survival of extravasated cancer cells (circulating tumor cells; CTCs) [15], the colonization capacity of CTCs [16], the number of CTCs expressing the membrane protein Thy-1 (CD90), a cancer stem/progenitor cell (CSPC) marker gene [17], and cancer cell mobility [18].