For that aim, SKBR3 ErbB2-positive breast cancer cells stably expressing either GFP (SKBR3-GFP) or GFP-nucleolin (SKBR3-NCL) were injected subcutaneously into female nude mice; once tumors formed (~4 days post injection), tumor volumes were measured every 2 days. The gene discussed is ERBB2; the disease is breast cancer.