The purpose of this study is to assess the efficacy, safety and tolerability of a therapy with EndoTAG-1 + paclitaxel in combination and EndoTAG-1 alone as a rescue therapy for patients with relapsed or metastatic triple receptor negative breast cancer (a special subgroup of breast cancer).

Breast cancer is still a major public health problem worldwide, as it is by far the most frequent neoplasm in women. In recent years so-called "profiling of breast cancer" with expression arrays has become common and it was suggested that the results will allow individualization of care. Breast cancer may now be subclassified into luminal, basal, and HER-2 subtypes with distinct differences in prognosis and response to therapy. About 80% of all basal-like-breast cancers possess a so-called "triple-receptor-negative" phenotype.

Patients with "triple receptor negative breast cancer" have a complete absence of hormone receptors incl. HER-2, an aggressive clinical course and a paucity of treatment options. The only therapeutic option is chemotherapy and in this respect the choice of cytostatic agents is limited. Against this background, the study tries to find another therapeutic option by combining a vascular-disrupting activity with the cytostatic effects of paclitaxel in the study drug EndoTAG-1.

Comparison: EndoTAG-1 + paclitaxel (combination therapy) and EndoTAG-1 (monotherapy) in comparison to paclitaxel (control group)

Inclusion Criteria:

• Histologically proven triple-receptor-negative metastatic or relapsed breast cancer
• Minimum interval of 6 months after the end of any previous taxane- containing chemotherapy regimen
• At least one tumor lesion measurable according to RECIST criteria
• Gender: female
• Age >= 18 years old
• Negative pregnancy test (females of childbearing potential)
• Willingness to perform double-barrier-contraception during study and for 6 months post chemotherapy treatment
• ECOG performance status 0, 1 or 2
• Signed informed consent

Exclusion Criteria:

• More than 1 previous chemotherapeutic treatment for metastatic or relapsed disease
• Major surgery < 4 weeks prior to enrollment
• Immunotherapy < 2 weeks prior to enrollment
• Severe pulmonary obstructive or restrictive disease
• Uncontrolled inflammatory disease (autoimmune or infectious)
• Clinically significant cardiac disease (NYHA stadium > 2)
• Laboratory tests (hematology, chemistry) outside specified limits
• Pregnancy or nursing status
• Known positive HIV testing
• Known hypersensitivity to any component of the EndoTAG-1 or taxane formulations
• History of malignancy other than breast cancer < 5 years prior to enrollment, except skin cancer (i.e. basal or squamous cell carcinoma) treated locally
• Known progressive cerebral metastasis (patients with cerebral metastases in a stable state or after successful surgical or radiological treatment are allowed to participate in the study)
• History of active or significant neurological disorder or psychiatric disorder that would prohibit the understanding and giving of informed consent, or would interfere in the clinical and radiological evaluation of central nervous system during the trial
• Concurrent treatment with other experimental drugs. Participation in another clinical trial with any investigational not marketed drug within 30 days prior to study entry