To understand how ICAM1 mediates tumor cell aggregation, we first investigated if tumor cells express the known ligands of ICAM1, LFA1 (CD11a/CD18), and MAC1 (CD11b/CD18), both of which belong to the beta 2 integrin family (ITGB2, CD18) and are normally expressed on leukocytes30. This evidence concerns the gene ITGAM and neoplasm.