Fig. 2: ER⁺ metastatic lesions are dormant.

a Representative fluorescence stereo micrographs of lungs from ≥ 3 mice with BT20, HCC1806, MCF-7, or T47D intraductal xenografts, arrows point to DTCs. Scale bar, 1 mm. b, c Representative micrographs of H&E stained lung sections from 3 mice bearing BT20 and HCC1806 (b) or MCF-7 and T47D (c) intraductal xenografts. Scale bar, 50 µm. d, e Representative fluorescence stereo micrographs of the liver (d) and lungs (e) from ≥3 mice bearing T70 and METS15 MIND xenografts. Scale bars, 1 mm. f Representative micrographs of H&E stained lung sections from 3 mice bearing METS15 intraductal xenografts. Scale bars, 50 µm. g Percentage of Ki67⁺ cells in matched primary and lung sections from mice 5 weeks after intraductal injection of BT20 and HCC1806 cells, n ≥ 14 sections. h Bar graph showing Ki67 index of BT20 and HCC1806 lung lesions of different sizes. i Ki67⁺ index in matched primary tumor and lung sections from mice 5 months after intraductal injection of MCF-7, T47D, and METS15 cells as indicated. In g and i each data point represents ≥ 1,000 and 100 cells analyzed, mean ± SD from ≥3 mice/condition, respectively. g–h Data represent mean ± SD from 3 different hosts. Student’s unpaired t-test, two-tailed. j Scheme of FUCCI reporter. k Bar plot showing percentage of cycling and non-cycling cells in primary tumors and in lung micro-metastases in MCF-7 intraductal xenografts-bearing mice. Data represent mean ± SD from 3 host mice. Paired t-test. l Representative fluorescence micrographs of MCF-7:FUCCI cells in matched primary tumor (left) and lung (right). Scale bars, 50 µm. m Bar plot showing the percentage of p27⁺Ki67- cells over total human cells in the lung. Data represent mean ± SD from n ≥ 3 mice, and dots represent ≥40 cells analyzed. One-way ANOVA. n Representative immunofluorescence micrographs for CK8 (blue), p27 (magenta) and Ki67 (cyan), counterstained with DAPI (gray) on lung section from MCF-7-bearing mice. Scale bar, 50 µm; inlet, 20 µm. *, ***, ****, and n.s represent P < 0.05, 0.001, 0.0001, and not significant, respectively.