To investigate the contribution of MUC5B to the growth and dissemination of human breast cancer cells in vivo, SCID-Beige mice were injected s.c. with either the Mini5B–Luc MCF7 clone or Mini5B–Luc empty shRNA MCF7 cell population or Mini5B–Luc CYS shRNA MCF7 cell population or the Ires–Luc MCF7 clone. The gene discussed is MUC5B; the disease is breast cancer.