The mouse mammary carcinoma 4T1 cells in the present study showed remarkable resistance to DOX (Fig. 2c, e and Additional file 1: Fig. S3) and two mechanisms of resistance have been clearly identified i.e. induction of P-gp mediated drug export and upregulation of the pro-survival, anti-apoptotic interleukin 6 (IL-6) (Figs. 4, 5, 6). This evidence concerns the gene PGP and breast carcinoma.