Antitumor effect of radioimmunotherapy in a mouse model of testicular tumor with micrometastases defined by polymerase chain reaction

The efficacy of radioimmunotherapy (RIT) was evaluated by using a mouse model of testicular tumor with macro- and micrometastases to various organs. RIT consisting of a single intravenous injection of 5.8 MBq of I-131-labeled anti-placental alkaline phosphatase (PLAP) MAb was conducted one day or 7 days after testicular implantation in SCID mice of HeLa Hep2 cells expressing PLAP. RIT antitumor effect was significant for primary tumors as well as micrometastases defined by polymerase chain reaction (PCR) assay. However, ablation of tumor cells could be achieved with this treatment only at the initial stage of tumor growth in the testis, when metastasis could also be prevented. Once micrometastasis had occurred, however, complete elimination of tumor cell(s) was difficult. These findings appear to have implications for the use of RIT in treatment for micrometastasis, especially when detectable only by PCR assay.