To know the role of circHIF1A in breast cancer cell plasticity by CD44, breast cancer cells were in the presence of hypoxic CAFs exosomes with down-regulation of circHIF1A or CD44 overexpression in breast cancer cells, and cell survival ability was assayed by CCK8 and it was found that cell survival ability was suppressed in the MDA-MB-231 and SKBR3 cells with circHIF1A shRNA exosomes derived CAFs and CD44 could rescue the progression partially (Fig. 6A, B). This evidence concerns the gene CD44 and breast cancer.