The purpose of this study is to test any good and bad effects of the study drug 131I-omburtamab. 131I-omburtamab could prevent the cancer from returning, or delay the cancer from getting worse, but it could also cause side effects. Researchers hope to learn more about how 131I-omburtamab works in the body, and how effective it is in treating cancer. 131I-Omburtamab is not approved by the FDA to treat DSRCT or other cancers of the peritoneum.

Inclusion Criteria:

• Have the diagnosis of DSRCT confirmed at MSKCC

• Age >1 year and able to cooperate with radiation safety restrictions during therapy period.

• Prior to intraperitoneal catheter placement

  • At least 1 weeks must have elapsed since prior chemotherapy
  • At least 2 weeks must have elapsed since biologic therapy
  • Toxicities of prior therapy must have resolved to grade 1 or less or to the patient's baseline

At the completion of surgery, patients must fulfill all of the additional following criteria:

• Have no definitive radiological evidence of disease active in liver or outside the abdomen/pelvic OR have had GTR of this disease at the time of catheter placement

Exclusion Criteria:

• Prior progression of disease
• Prior hypothermic intraperitoneal chemotherapy (HIPEC)
• Cardiac, pulmonary, and neurologic toxicities are greater grade 1 per NCI CTCAE version 5
• Renal, gastrointestinal, and hepatic, toxicities are greater than grade 2 (per NCI CTCAE version 5)
• History of allergy to mouse proteins
• Patients with grade 4 hypersensitivity reaction to radiolabeled iodine

Memorial Sloan Kettering Cancer Center supports the international committee of medical journal editors (ICMJE) and the ethical obligation of responsible sharing of data from clinical trials. The protocol summary, a statistical summary, and informed consent form will be made available on clinicaltrials.gov when required as a condition of Federal awards, other agreements supporting the research and/or as otherwise required. Requests for deidentified individual participant data can be made beginning 12 months after publication and for up to 36 months post publication. Deidentified individual participant data reported in the manuscript will be shared under the terms of a Data Use Agreement and may only be used for approved proposals. Requests may be made to: crdatashare@mskcc.org.