• Desmoplastic Small Round Cell Tumor
• Peritoneal Cancer
• Peritoneal Carcinoma

• Drug: 131 I-omburtamab
  Single dose of IP RIT administered through an IP catheter with 131 I-omburtamab at 80mCi/m2
• Radiation: WA-IMRT
  Group A participants will receive WA-IMRT approximately 2-4 weeks after completing IP RIT. A dose of 30 Gy will be delivered in 20 fractions of 1.5 Gy given once daily, 5 days per week over the course of approximately 4 weeks
  Other Name: Intensity Modulated Radiation Therapy

• Experimental: Group A
  Participants with DSRCT who have undergone GTR of their abdominopelvic disease and who have no definitive radiological evidence of disease in liver or outside the abd/pelvis. Patients if deemed of likely benefit to the patient after completing RIT plus WA-IMRT, or will be mandated if ANC is persistently <500/ul despite use of G-CSF for >1 week, or if patients experience life threatening febrile neutropenia.
  Interventions:

  • Drug: 131 I-omburtamab
  • Radiation: WA-IMRT
• Experimental: Group B
  Participants with DSRCT without GTR
  Intervention: Drug: 131 I-omburtamab
• Experimental: Group C
  Participants with tumors other than DSRCT and will be enrolled onto an assessment arm to determine eligibility. Immunohistochemistry to assess B7H3 expression will be performed on frozen or paraffin embedded tissue using omburtamab (frozen tissue) or a commercially available anti-B7H3 antibody (if paraffin embedded).
  Intervention: Drug: 131 I-omburtamab

Inclusion Criteria:

Inclusion Criteria for All Patients:

• Age >1 year and able to cooperate with radiation safety restrictions during therapy period.
• Minimum life expectancy of eight weeks as determined by consenting professional
• Signed informed consent indicating awareness of the investigational nature of this program

• Prior to intraperitoneal catheter placement

  • At least 2 weeks must have elapsed since prior chemotherapy, radiotherapy or biologic therapy
  • Toxicities of prior therapy must have resolved to grade 1 or less

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

Group A patients:

• Have the diagnosis of DSRCT with peritoneal involvement, confirmed at MSK
• Have undergone GTR of abdomino-pelvic disease, as per surgeon's report
• Have no definitive radiological evidence of disease active in liver or outside the abdomen/pelvic
• Should not have had prior WA-IMRT
• Stem cells: Patients must have an autologous hematopoietic stem cell product cryopreserved and available for re-infusion after 131 I-omburtamab treatment. The minimum dose for hematopoietic stem cells is 2 x 10^6 CD34+ cells/kg

Group B patients:

• Have the diagnosis of DSRCT with peritoneal involvement, confirmed at MSK
• Have radiological evidence of disease (does not need to be in the abdomen)

Group C patients:

• Have the diagnosis of tumors other than DSRCT, confirmed at MSK
• Have a tumor that involves the peritoneum
• Omburtamab reactivity must be confirmed by immunohistochemistry except for tumors with a reported incidence of B7H3 expression of >70%: these include neuroblastoma, melanoma, Ewing's family of tumors, rhabdomyosarcoma, osteosarcoma, Wilm's tumor, hepatoblastoma and rhabdoid tumor (testing for these histologies may be performed if desired at the discretion of the investigator and after discussion with the prinicipal investigator)
• May or may not have radiological evidence of disease
• <20% chance of long term disease-free survival

Exclusion Criteria:

• Prior therapy: Less than 3 weeks between any last chemotherapy, radiotherapy or biologic therapy and 131I-omburtamab infusion date (ie at least 3 weeks must separate prior therapies and ombutamab infusion date).
• Severe major organ toxicity. Cardiac, pulmonary, and neurologic toxicity should all be grade 1 or less; Renal, gastrointestinal and hepatic, toxicities should all be grade 2 or less (per NCI CTC version 5)
• Platelet count should be >50,000/ul and hemoglobin should be >8gm/dl. Platelet transfusions are not permitted within one week for blood count demonstrating platelet count >50,000
• Patients with clinically suspected dense intraperitoneal adhesions preventing adequate IP distribution
• History of allergy to mouse proteins
• Patients previously treated with murine monoclonal antibodies will be excluded if they have a HAMA level of >1000U/ml (defined as positive).
• Active serious infections not controlled by antibiotics
• Patients with grade 4 hypersensitivity reaction to radiolabeled iodine
• Patients who have received live viral vaccines within 30 days before the first dose of study treatment (patients are NOT permitted to receive viral vaccines while participating in the study)
• Pregnant women and women who are breast feeding are excluded for fear of danger to the fetus/infant. Therefore, negative pregnancy test is required for all women of child-bearing age, and appropriate contraception is used during the study period and for 12 months following therapy. Pregnancy testing will be carried out within two weeks prior to administration of radioiodinated omburtamb in females of childbearing age.
• Inability or unwillingness to comply with radiation safety procedures or protocol requirements.