Although the subclones of E0771 and other breast cancer cells that express ICAM-1 like 4T1 can establish extravascular metastasis in immunocompetent mice (26, 73), it appears that the parental E0771 cells we have used represent a major subgroup of breast tumor–derived CTCs capable of growing inside the lung vasculature (71). The gene discussed is ICAM1; the disease is breast cancer.