Inclusion Criteria:

        For Phase I :

          -  Histologically or cytologically confirmed metastatic breast cancer, refractory to any
             standard therapy or for which the standard therapy is considered unsuitable;

          -  Patient must have at least one evaluable or measurable metastatic lesion (lesions as
             defined by revised Response Evaluation Criteria in Solid Tumors).

        For Phase II :

          -  Histologically or cytologically confirmed advanced inoperable triple negative breast
             cancer with no prior anticancer therapy regimen in metastatic setting;

          -  Patient with a minimum washout period of 12 months following previous taxane based
             adjuvant therapy;

          -  Patient must have at least one measurable metastatic lesion. Ascites, pleural
             effusion, and bone metastases are not considered measurable;

          -  Acceptance of pre-treatment metastatic biopsies for all patients and on-treatment
             metastatic biopsies in selected centres.

        For the whole study:

          -  Male or female subjects aged ≥ 18 years old, or legal age of the majority in the
             country;

          -  Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1;

          -  Estimated life expectancy of at least 3 months;

          -  Adequate haematological function based on the last assessment performed within 7 days
             prior to the first IMP (investigational medicinal product) administration;

          -  Adequate renal function based on the last assessment performed within 7 days prior to
             the first IMP administration;

          -  Adequate hepatic function based on the last assessment performed within 7 days prior
             to the first IMP administration;

          -  Female participant of childbearing potential must have a negative pregnancy test
             (serum) within 7 days prior to the first day of test drug administration. Effective
             contraception both for female patients of childbearing potential and male patients
             with parteners of childbearing potential.

        Exclusion Criteria:

          -  Other active malignancy within the last 3 years (except for basal cell carcinoma or a
             non-invasive/in situ cervical cancer or intra-mucosal gastro-intestinal cancers that
             were treated curatively);

          -  Presence of grade ≥ 2 toxic effects (excluding alopecia) due to prior cancer therapy;

          -  Known hypersensitivity to the IMP (S 81694 and paclitaxel) or their excipients;

          -  Evidence of peripheral neuropathy of grade 2 or higher;

          -  Participant previously received paclitaxel and discontinued due to toxicity related to
             paclitaxel;

          -  Participant known as refractory to taxanes;

          -  Any prior cancer therapy within 4 weeks or 5 half-life (whichever is the shorter)
             before the first IMP administration;

          -  Participant with current, serious, uncontrolled infections;

          -  Participant with brain metastasis or leptomeningeal metastasis (except patients with
             brain metastasis that have been stable post-radiation therapy and who are off steroids
             for > 2 months);

          -  History of cardiac disease;

          -  Uncontrolled arterial hypertension;

          -  Presence of risk factors for torsades de pointes (e.g. heart failure, hypokalaemia,
             family history of long QT syndrome);

          -  Any clinically significant medical condition (e.g. organ dysfunction) or laboratory
             abnormality likely to jeopardize the patient's safety or to interfere with the conduct
             of the study, in the investigator's opinion.