The expression of phospho-p90RSK in various breast cancer cell lines and doxorubicin sensitivity. The levels of protein expression of phospho-p90RSK and total p90RSK were examined in 11 breast cancer cell lines (a). The scattered plot for correlation analysis between relative phospho-p90RSK expression and sensitivity to doxorubicin is shown (b). Cell survival* denotes for the proportion of cancer cells surviving after doxorubicin 10uM treatment. The expression status of ER and HER2 in various breast cancer cell lines was determined by the works of **Subik et al.  and ***Neve et al. .