Phosphoproteomic analysis was performed to decipher changes occurring in tumour cells after treatment with conditioned media from endothelial cells, which may protect them from doxorubicin damage, and promote resistance to the treatment. Briefly, MMTV-PyMT (mouse mammary tumour virus-polyoma middle tumour-antigen) derived tumour cells were pretreated with conditional media from endothelial cells isolated from MMTV tumours treated with doxorubicin for 24 hours, andthen treated afterwards with vehicle (PBS) or doxorubicin in culture for 45 minutes and 2 days.