In this ground-based mouse model study, we exposed female ApcMin/+ mice to GCRsim at NASA’s Space Radiation Laboratory (NSRL) and focused on understanding the roles of PER, ERRα, and SPP1 signaling in GCRsim-exposed ApcMin/+ mice to elucidate their contributions to breast cancer development. The gene discussed is ESRRA; the disease is breast carcinoma.