Background:Serum cathepsin B activity has been considered a potential marker of tumor progression. We previously demonstrated that low-frequency electromagnetic stimulation (LF EMS), called bioresonance therapy (BRT), may both accelerate and inhibit the growth of transplantable hepatoma (Morris type 5123D), including total tumor regression. The aim of this study was to assess serum cathepsin activity during tumor progression and regression.Material/Methods: Of 60 female rats inoculated with Morris hepatoma cells, 45 were treated with BRT, and the remaining 15 were left without treatment. Fifteen rats without inoculated tumors served as controls. Serum cathepsin B activity was determined, tumor volumes were measured, and histological examinations of the tumor tissues were performed.Results: Of the 45 BRT-treated rats, tumor regression was observed in 31 rats, and serum cathepsin activity was analyzed in these rats. In all non-treated rats, tumor progression was observed. Serum cathepsin B activity was significantly higher in both the BRT-treated group (27.8±4.1 U/I,p<0.01) and the tumor-bearing group (19.9±2.5 U/l, p<0.05), as compared to the controls (13.3±3.4U/l).
Conclusions: Cathepsin B may play an important role, not only in tumor expansion, but also during the processes of cancer cell death and resorption. High circulating levels may thus correspond to effective therapeutic response in the course of antitumor treatment.

Keywords: Cathepsin B - blood, Cell Death, Cell Division, Disease Progression, Electromagnetics, Liver Neoplasms, Experimental, Necrosis, Neoplasm Transplantation, Tumor Markers, Biological, Cathepsin B - blood, Cell Death, Cell Division, Disease Progression, Electromagnetic Phenomena, Liver Neoplasms, Experimental, Necrosis, Neoplasm Transplantation, Tumor Markers, Biological