ICAM1 and neoplasm: Intravascular nature of the tumor could be explained by two factors: (1) tumor cells lack CD29 (β1 integrin) and CD54 (intercellular adhesion molecule- (ICAM-) 1), which are essential for lymphocyte homing and transvascular migration; (2) aberrant expression of CD11a and CD49d (very late antigen- (VLA-) 4) on tumor cells enables them to stay in the luminal space via attachment to endothelial cells.