In the present study we investigated the effects of calcitriol alone or in combination with astemizole on tumor growth in an in vivo preclinical model using athymic mice xenografted with two different human breast cancer cell lines: T-47D (ERα, VDR and EAG1 positive) and a ductal infiltrating carcinoma breast cancer-derived primary cell culture (MBCDF, ERα negative, VDR and EAG1 positive)[22]. The gene discussed is ESR1; the disease is breast cancer.