Cellectar Biosciences, Inc. announced that iopofosine I 131 in combination with external beam radiation therapy (EBRT) was safe and tolerated in a SPORE Grant supported investigator-initiated Phase 1 clinical trial. The twelve patients treated for locoregionally recurrent head and neck squamous cell carcinoma previously received chemoradiation alone (42%), surgery (58%) or surgery combined with radiation or chemoradiation (92%). The data were presented in a poster at the 2024 Multidisciplinary Head and Neck Cancers Symposium held February 29-March 2, 2024, in Phoenix, AZ.

Complete remission was achieved in 64% of patients, with an ORR of 73% (n=11). Prior to treatment with iopofosine I 131, six patients had multiple recurrence and one had metastatic disease both of which are indicative of poor outcomes. Additionally, the study demonstrated durability of tumor control with an overall survival of 67% and progression free survival of 42% at 12 months.

The patients received two therapeutic doses of iopofosine I 131 at a fixed fractionated dose of 15.6 mCi/m2 (days 1 and 8) with SPECT/CT imaging performed to quantitate the biodistribution of iopofosine I 131. Patients subsequently received EBRT to complete the designated radiation dose outlined in the reirradiation plan, which was 60-70 Gray. Overall, eleven patients (92%) experienced a treatment-related adverse event.

The most common treatment-related adverse events of any grade were thrombocytopenia (92%), lymphopenia (75%), neutropenia (75%), and anemia (92%). Observed adverse events were consistent with the known toxicity profile of iopofosine I 131, with cytopenias being the most common with all patients recovering.