CD44 and breast carcinoma: Interestingly, compared with those in paclitaxel‐sensitive cells, the expression levels of ERα and CD44 were also increased in paclitaxel‐resistant cells (Figure 4E and F), suggesting that ERα and CD44 are up‐regulated by paclitaxel and might be involved in the acquisition of the drug resistance phenotype in ERα+ breast cancer cells.