Breast cancer is known as the most common malignant disease among women . Conventional therapy for breast cancer comprises several treatment approaches including surgery, radiation or systemic therapy. Hormonal and targeted therapy, immunotherapy and chemotherapy are part of systemic therapies and their specific use depends on several tumor features like hormone receptor status, tumor molecular portrait, stage of the tumor and others . However, chemotherapy often remains a standard treatment option for some of the breast cancer patients. Common chemotherapeutic drugs used for the treatment of breast cancer include anthracyclines like doxorubicin or cyclophosphamide and taxanes like paclitaxel or docetaxel . Doxorubicin is topoisomerase II inhibitor and anthracycline which functions trough intercalation into DNA causing DNA double strand breaks. Paclitaxel stabilizes polymerization of microtubules resulting in cellular mitotic arrest and disruption of mitosis . Although chemotherapy is a common therapeutic choice for the cancer treatment, resistance to the therapy represents one of the major clinical challenges. More detailed elucidation of the mechanisms of cancer chemotherapy resistance is therefore of great clinical relevance. Aim of the presented work was to establish breast cancer therapy-resistant cell lines with acquired resistance towards selected chemotherapeutic drugs (doxorubicin and paclitaxel). Chemotherapy-resistant cells were derived from commonly used breast cancer cell lines (MDA-MB-231, JIMT-1, T47D) by culturing cells with continuously increasing concentrations of chemotherapeutic drugs doxorubicin or paclitaxel. Increased resistance towards selected chemotherapeutic agents in parental and derived resistant breast cancer cells was confirmed by cell viability assay and increased resistance of the cells was observed even after one month of culture without chemotherapy. Tumorigenicity of derived resistant breast cancer cells was characterized by in vivo experiments. Established resistant cell models therefore represent potential tool for studying chemotherapy resistance in breast cancer and will be used to assess changes underlying chemotherapy resistance in future experiments.