AACR 2018 — 124I-8H9-directed radioimmuno-PET shows promise in DSRCT


  • Hao Cheng, MD
  • Univadis
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Takeaway

  • 124I-8H9-directed radioimmuno-PET is safe, distributes well, and shows activity against micro-metastatic desmoplastic small round cell tumor (DSRCT).

Why this matters

  • DSRCT is a rare sarcoma with a long-term survival of
  • The murine monoclonal IgG1 antibody 8H9 recognizes cell surface antigen 4Ig-B7H3 and binds to 96% of DSRCTs with restricted normal tissue reactivity.
  • This is a phase I study of radioiodinated 8H9 to evaluate toxicity, pharmacokinetics, biodistribution, and efficacy.

Study design

  • Cohorts of 3-6 patients were treated with escalated doses of IP 131I-8H9.
  • A prior dose of 2mCi 124I-8H9 IP was used to acquire PET images and biodistribution data.
  • Toxicity was monitored clinically and biochemically.

Key Results

  • 41 DSRCT patients received doses of 30-90mCi/m2.
  • No dose-limiting toxicities.
  • Blood and peritoneal half-times were 32.5h and 14.6h, respectively. 
  • Median PFS from radioimmunotherapy (RIT) for first remission patients (n=21) undergoing gross total resection followed by RIT and whole-abdominal radiotherapy was 17.9±1.7 months.
    • Only 9 patients have relapsed.
  • In contrast, patients with gross residual disease pre-RIT or those receiving RIT in ≥2nd remission (n=20) had median PFS of 8.1±3.5 months (P<.05 for pfs and os>
  • Recommended phase II dose was 80mCi/m2.

Limitations

  • Phase 1 study, heterogeneous population.
  • Could not evaluate disease responses.

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