In a preclinical model of human luminal breast cancer, intact female wild-type (129S6/SvEv) mice were injected s.c. with either SSM2 (spontaneous signal transducer and activator of transcription 1-deficient (STAT1–/–) mammary) or SSM3 tumor cell lines, derived from primary STAT1–/– spontaneous tumors, into the right thoracic mammary fat pad. The gene discussed is STAT1; the disease is breast cancer.