Tumor-associated thymidine kinase in the sera of rats with transplanted hepatomas

A cytoplasmic form of thymidine kinase was detected in sera from rats bearing Morris hepatoma 7777. Polyacrylamide electrophoretic properties demonstrate similarity between the serum enzyme extracted from hepatoma tissue. This form of thymidine kinase has also been described in normal human fetal tissue and a variety of human tumor cells. The results suggest that serum isoenzymes of thymidine kinase may be a useful adjunctive test for the presence of certain types of malignant tumors.