Serum activities of dipeptidyl-
aminopeptidases (
DAP) II and IV were measured in
tumor-bearing animals and in patients with blood and solid
cancers using highly sensitive and specific fluorometric methods. In mice with intraperitoneal or subcutaneous implantation of
Ehrlich ascites tumor cells, serum
DAP II activity was increased and serum DAP IV activity was decreased, resulting in a significant increase in the ratio of serum
DAP II and DAP IV activities. The increase in the ratio of these two activities paralleled the size of the subcutaneous
tumors. However, both serum
DAP II and DAP IV activities were increased in rats with experimental
hepatic cancer induced by
3'-methyl-4-dimethylaminoazobenzene, and the increase in the ratio of the two activities was not significant. In
cancer patients, as compared with healthy subjects, serum
DAP II activity was increased and serum DAP IV activity was decreased, the ratio of serum
DAP II and DAP IV activities being markedly increased in
cancer patients. Both serum
DAP II and DAP IV activities were increased in patients with
hepatic cancer as were those in rats with
hepatic cancer, but the increase in
DAP II was greater than that of DAP IV; thus the ratio of the two activities increased significantly. These data suggest that the increase of the serum
DAP II/DAP IV ratio could be a biochemical index of
cancer.