The present invention relates to compositions comprising a specific p38α inhibitor and an agent that induces chromosome instability, wherein the specific p38α inhibitor has a half maximal inhibitory concentration (IC50) equal to or less than 40 nM. The invention also relates to the above compositions or to a specific p38α inhibitor for use in the treatment of breast cancer, wherein the breast cancer is characterised by a high degree of aneuploidy. Finally, the invention relates to a method for identifying a breast cancer patient who responds to a treatment with the above compositions or with a specific p38α inhibitor, wherein the breast cancer is characterised by a high degree of aneuploidy, and a method for selecting a treatment for a breast cancer patient.