B2M and neoplasm: Expression of human beta-2-microglobulin (B2M), a human housekeeping gene17,30, was detected in bone homogenates from MCF7-inoculated mice in 5/10 (50%) −E2 mice and 5/8 (63%) +E2 mice (Fig. 3g and Supplementary Fig. 3) by qPCR, making this the second most sensitive method of MCF7 tumor cell detection in bone after flow cytometry.