Inclusion Criteria:

- Male or female patients, age ≥ 18 years.

- Histologically confirmed progressive synovial sarcoma with a minimal total tumor
volume of 65mL at the time of inclusion.

- Frozen or paraffin-embedded tumor samples for immunohistochemical analysis are
mandatory for registration in this study.

- Patients with doxorubicin- and ifosfamide-resistant synovial sarcoma (defined as
patients with progression under doxorubicin and ifosfamide treatments or with rapid
progression (i.e. within 4 months) after the last dose of doxorubicin and ifosfamide,
or patients previously treated with doxorubicin and ifosfamide and with disease
progression on another regimen of chemotherapy for advanced disease).

- Patients must have disease not amenable to surgery, radiation or combined modality
treatment with curative intent.

- At least one measurable site of disease as defined by RECIST criteria 1.1.

- ECOG performance status of 0, 1, 2.

- Life expectancy ≥ 3 months.

- Left Ventricular Ejection Fraction (LVEF)> 50% as assessed by MUGA scan or ECHO at
screening.

- Normal pulmonary function with Force Vital Capacity (FVC) of at least 60% and DLCO of
at least 50%.

- Adequate bone marrow, liver and renal function including the following:

- Absolute neutrophil count ≥ 1.5 G/L, platelet count ≥ 100 G/L, and hemoglobin ≥
10 g/dL)

- AST/ALT ≤ 3 x upper limit of normal (ULN) (or ≤ 5.0 x ULN if liver metastasis)
and total bilirubin ≤ 1.5 x ULN (≤ 2.5 x ULN if liver metastases),

- Serum creatinine ≤ 1.5 x ULN or creatinine clearance ≥ 50 mL/min according to
Cockroft formula.

- Adequate contraceptive methods for the whole duration of the study and for up to 12
months after the last study drug administration.

- Mandatory affiliation with a health insurance company.

- Patients must provide written informed consent before any study specific procedures
or assessments, and must be willing to comply with follow up assessments and
procedures.

Exclusion Criteria:

- Chemotherapy within the last 4 weeks before inclusion; radiotherapy, or any other
investigational agent within 14 days or 5 half-lives, whichever is longer prior to
the first dose of study drug.

- Positive human anti-mouse antibody (HAMA) or human anti-chimeric antibody (HACA)
response. HAMA/HACA assays will be performed only for patients previously treated by
monoclonal antibodies.

- Uncontrolled arterial hypertension: systolic blood pressure ≥ 140 mmHg or diastolic
blood pressure ≥ 90 mmHg or both despite appropriate therapy.

- Patients with brain metastases.

- Previous history of high-dose chemotherapy with stem cell rescue.

- Chronic use of immunosuppressive drugs such as systemic corticosteroids.

- Previous therapy with monoclonal antibodies within 4 months before study entry.

- Clinically significant abnormal ECG (i.e. > grade 1) at inclusion.

- Prior history of other malignancies other than synovial sarcoma (except for basal
cell or squamous cell carcinoma of the skin or carcinoma in situ of the cervix)
unless the subjects has been free of the disease for at least 3 years.

- No resolution of all specific toxicities (excluding alopecia) related to any prior
anti-cancer therapy to Grade ≤ 1 according to the NCI CTCAE v4.

- Known immediate or delayed hypersensitivity reaction to 111In, 90Y, DTPA or any
excipients of the investigational product.

- Psychological, familial, sociological, or geographical conditions that would limit
compliance with study protocol requirements.

- Pregnant and breastfeeding women are ineligible.