Radioimmunotherapy with 131I-L19SIP (Radretumab) in metastatic solid tumors: Preliminary results

Objectives This study involves radioimmunotherapy (RIT) with the human antibody L19SIP(Radretumab) labeled with 131I in combination with Whole Brain Radiation Treatment (WBRT). Our aim was to evaluate selective uptake of 124I-L19SIP in subjects with brain metastatic lesions.

Methods We studied 4 patients (3F e 1M; 3 breast and 1 lung cancer) with inoperable brain and extracranial metastases (diameter >10 mm). All underwent PET/CT scans (whole body and brain; SIEMENS Biograph Hi-Rez) with 18F-FDG (5 MBq/kg; acquisition time: 1h after e.v.) and 124I-L19SIP (mean administered dose 159MBq; acquisition time: 4h, 24h, 48h, 72h and 96h) for diagnostic and dosimetric purpose. The subjects were enrolled for RIT when the target/background uptake ratio of brain metastases was >4 and bone marrow dose was <2 Gy. All patients were then treated with 131I-L19SIP (4.107 GBq/m2 ); the distribution of the therapeutical agent was evaluated with SPECT and Whole Body scan 24 and 48 h. after administration. 18F-FDG scan was repeated for the follow up after 2-4-6 months.

Results Globally the 14 brain lesions had high FDG (mean SUV 8.39) and 124I-L19SIP uptake. After RIT, the metastases uptake during the FDG follow up (6 months) was progressively reduced in one patient (-51%). A second patient had -65% SUV after 4 months. A third one had -42% at the first assessment (2 months). The last one died before the first PET control, due to pulmonary infection. Similarly the extracranial localizations, with high 124I-L19SIP uptake at the basal scan, showed a significant SUV reduction after RIT.

Conclusions Our study indicates that RIT with Radretumab is a promising tool for therapy of solid tumors. The significant reduction of glucose metabolism in the lesions suggests the potential clinical efficacy of L19SIPI131 therapy. More data are necessary to confirm these preliminary results, particularly in patients with lower stage of disease