HIF1A and columnar cell hyperplasia of the breast: HIF-1α protein expression was significantly higher in the CCH groups, especially in CCH 8W group than in the sham group (F = 17.53, P < 0.01; Sham vs. CCH 4W, *P < 0.05; Sham vs. CCH 8W, ##P < 0.01; CCH 4W vs. CCH 8W, &P < 0.05) (Figure 5B), indicating the presence of CCH in the BCCAO rats.