In preclinical breast cancer models, evidence suggests that aberrant expression of VCAM-1 on metastatic breast cancer cells in the lungs attracts VLA-4+ macrophages (MACs) into the metastatic tumor niche, whereas the primary, non-metastatic breast cancer cells in the mammary gland express little to no VCAM-1 on their surface. Here, VCAM1 is linked to breast carcinoma.