In this study, results of the groupwise statistical comparisons suggest the existence of at least two different IDO1-associated molecular profiles in rabbit mammary carcinoma, i.e., (1) tumors with IDO1 expression in >10% of tumor cells, higher ER-α status, lower mitotic counts, as well as decreased histological scores and grades and (2) tumors with IDO1 expression in <10% of tumor cells, reduced ER-α levels, higher mitotic counts, as well as increased histological scores and grades. The gene discussed is ESR1; the disease is neoplasm.