Calphostin C is used to treat subjects for cancer which is resistant to treatment by other forms of chemotherapeutic drugs, for example breast or uterine cancer, or other cancers characterized by tumor cells that have a defect in an apoptotic regulatory pathway which renders said cells resistant to at least some other forms of chemotherapeutic treatment. The other chemotherapeutic drug used with calphostin C is selected from the group comprising taxanes and anthracyclines, such as paclitaxel or doxorubicin. The use may take the form of administering calphostin C and then subjecting the patient to photodynamic therapy (PDT).