Fig. 4: Loss of TET2 expression promotes tumorigenesis and tamoxifen resistance in vivo.

a Representative immunostaining images of H&E, Cre, Ki67, and ERα in mammary glands of 5-week-old Tet2^f/+;PyMT (WT-PyMT) and MMTV-Cre;Tet2^f/+;PyMT (MUT-PyMT) female mice. Arrow indicating premalignant hyperplasia morphology (scale bar: 50 μm). b Flow cytometry analysis showing the percentage of basal MaSC-enriched population (MaSCe, Lin^-CD24⁺CD29^hi, indicated by a red circle and luminal cell population (Lum, Lin⁻CD24⁺CD29^lo, indicated by a blue circle) isolated from 6-week-old WT-PyMT and MUT-PyMT female mice (n = 3 animals/group). c Representative immunofluorescence images showing co-staining of CK8 (red) and CK14 (green) in mammary glands of 7-week-old WT-PyMT and MUT-PyMT female mice (scale bar: 50 μm), and d bar graphs showing percentage of CK14⁺CK8⁻, CK14⁻CK8⁺, and CK14⁺CK8⁺cells. n = 8 data points analyzed from eight independent tissue section staining images of two animals for each group. Data were presented as mean ± SD. p-values were determined by two-sided Student’s t-test between the indicated two groups; asterisk indicates p < 0.05. e Tumor size of all the tumors collected from WT-PyMT and MUT-PyMT female mice at 12–13 weeks of age. n = 11 WT-PyMT tumors and n = 19 MUT-PyMT tumors were collected from three animals for each group. Data were presented as mean ± SD. p-values were determined by two-sided Student’s t-test between the indicated two groups; asterisk indicates p < 0.05. f Lung tissues from WT-PyMT and MUT-PyMT female mice at 5 weeks and 8 weeks of age (scale bar: 50 μm). The black ellipse indicating metastasis foci. g Bar graph showing number of histologically identified metastasis loci per lung/animal (n = 5 animals/group). Data were presented as mean ± SD. p-values were determined by two-sided Student’s t-test between the indicated two groups; asterisk indicates p < 0.05. h, i Tumor size and tumor phenotype of 7-week-old WT-PyMT and MUT-PyMT female mice that had been treated with mock control vehicle, corn oil, or tamoxifen (i.p. 25 mg/kg) daily for 5 consecutive days per week for 4 weeks (n = 6 animals/group). Arrow indicating normal single-layered ductal epithelial morphology (scale bar: 100 μm). Data were presented as mean ± SD. p-values were determined by two-sided Student’s t-test; asterisk indicates p < 0.05. j Representative immunostaining images of TET2 and ERα, and k Chi-Square analysis of TET2 and ERα expression in 83 human breast tumor specimens of luminal breast cancers and triple negative breast cancers. (−): negative/low staining, (+): positive/high staining (scale bar: 50 μm). Asterisk indicates p < 0.05; double asterisks indicate p < 0.01. Source data are provided as a source data file.