To further determine whether increased sensitivity to limited amounts of estrogen could allow SSM2 tumor engraftment in male mice and/or following OVX, we administered the aromatase inhibitor Letrozole (AI, 10 ug/ day) to ovariectomized animals for 4 weeks and examined the extent of tumor growth in bone by histological analysis. The gene discussed is CYP19A1; the disease is neoplasm.