Some of the raw materials for the investigational drug are difficult to obtain and expensive.

The purpose of this study is to evaluate safety and pharmacokinetics as well as the biodistribution of OTSA101-DTPA-111In and to evaluate the safety of intravenous administration of OTSA101-DTPA-90Y.

Inclusion Criteria:

1. Patients with a documented relapsed or refractory synovial sarcoma after standard chemotherapy
2. Patients ≥18 years of age at the time of obtaining informed consent
3. Patients with an Eastern Cooperative Oncology Group (ECOG) performance status (PS) of 0 or 1
4. Patients with measurable lesion
5. Patients not received any anti-malignancy agent or specified surgical intervention within 28 days or specified radiotherapy within 14 days prior to study registration.
6. Patients without any clinically significant laboratory abnormality.
7. Patients with adequate heart function as measured by echocardiography or multiple gated acquisition scan (MUGA).
8. Patients with adequate pulmonary function as measured by pulmonary function tests.
9. Patients who are either not of childbearing potential or who agree to use a contraception method during the study and for 12 months after the last dose of study drug
10. Patients must be able to understand and be willing to sign a written informed consent

Exclusion Criteria:

1. Patients with documented concurrent malignancy.
2. Patients with brain metastasis with clinical symptoms.
3. Patients with any infection requiring systemic treatment.
4. Patients with lung inflammation or pulmonary fibrosis.
5. Patients with a known history of hypersensitivities to antibody agents or serum albumin agents.
6. Patients with a known history of autoimmune diseases.
7. Patients with myocardial infarction (MI) within 6 months prior to study registration.
8. Patients with uncontrolled diseases.
9. Patients with any disease requiring continuous systemic administration of steroids or immunosuppressants.
10. Patients with evidence of active HBV, HCV or HIV infection.
11. Pregnant or breastfeeding female patients, or female patients with suspected pregnancy.
12. Patients who are participating any other investigational treatments during the study.
13. Patients with psychiatric disorders and is considered to have difficulty to study participation.