When EO771 WT cells or EO771 Xkr8 KO cells were injected into mammary gland fat pads of C57BL/6 WT mice for longitudinal tumor volume studies (Fig. 2A), the Xkr8 KO tumors exhibited significant reduction in tumor growth compared to WT tumors, as evident by relative tumor volume (Fig. 2B), tumor weight (Fig. 2C) and spleen weight (Fig. 2D). The gene discussed is XKR8; the disease is neoplasm.