In contrast, another well-studied breast cancer line that metastasizes to lungs, 4T1, gave rise to spontaneous CTC generation in immunodeficient NSG mice as reported (39) (Supplementary Figure 6B), and all CTCs recovered from these mice expressed high levels of both ICAM-1 and the myeloid-specific chemokines we also found in E0771 cells (Supplementary Figures 3, 6, andSupplementary Table 1). Here, ICAM1 is linked to breast cancer.