Repeated anti-CEA-radioimmunotherapy (RAIT) with 131iodine-labetuzumab after resection of colorectal liver metastases (CLM): Long-term results of a prospective phase II study.

Abstract

719 Background: Previously, single anti-CEA-radioimmunotherapy (RAIT) with 131iodine(I)-labetuzumab after complete (R0) resection of CEA-positive CLM was well tolerated and improved overall survival (OS) compared to a control group without RAIT. In this phase II study, we examined safety, feasibility, and long-term efficacy of repeated RAIT in the same setting. Methods: After R0-resection of CEA-positive CLM, 63 pts (42 m, 21 f; median age, 64.5 yrs) with synchronous (n=33) or metachronous (n=30) CLM received RAIT with 40-50 mCi/m2 per dose. 45 pts were intermediate/high risk for early metastatic relapse according to the Fong score. Restaging with CT/MRI and FDG-PET was performed prior to each RAIT. Pts with persistent elevated serum CEA-levels or inconclusive lesions during post-operative restaging received RAIT, but were classified as “non-adjuvant.” Toxicity was classified according to NCI-CTC v2.0. Time to progression (TTP), OS and cancer-specific survival (CSS) were calculated. The median follow-up was 54 (range 6-127) mos. Results: After the first cycle of RAIT 14 of 63 pts experienced grade 4 hematological toxicity. Nineteen pts did not receive the second cycle of RAIT due to prolonged toxicity, impaired performance status (n=6), or metastatic relapse (n=13). The latter were further treated by resection (n=3) or systemic chemotherapy (n=10). Forty-four pts received the planned second cycle of RAIT. Of these, 4 pts newly experienced grade 4 hematological toxicity. For all 63 pts, the median TTP, OS and CSS were 13, 57 and 92 months, respectively. The truly “adjuvant” pts (n=39) had a an improved median TTP (26 vs. 6.6 mos, p<0.0001), OS (76 vs. 42 mos, p=0.03) and CSS (not reached vs. 42 mos, p=0.003) in comparison to “non-adjuvant” pts (n=24). Conclusions: Repeated anti-CEA-RAIT with 131I-labetuzumab is safe, feasible, and well-tolerated (100% compliance), with expected hematological toxicity. The long-term survival after RAIT is very encouraging, in particular for pts deemed truly “adjuvant” post-salvage resection of CLM at restaging prior to RAIT.