Thymidine kinase activities in mononuclear leukocytes and serum from breast cancer patients.

Levels of the nucleotide pathway enzyme thymidine kinase (TK) were assayed in the mononuclear leukocytes and serum of 70 female patients with breast cancer and 98 male and 77 female non-cancer hospital patients. The total TK levels in both mononuclear leukocytes and serum from patients with breast cancer were significantly higher than in controls. The serum TK levels showed a significant correlation with cancer stage. No such correlation was observed with mononuclear leukocyte TK levels. Serum TK from 20 patients with breast cancer and 19 control patients was further assayed to ascertain the relative contributions of the thymidine kinase isozymes TK1 and TK2 to total TK levels. The increase in serum TK from breast cancer patients appears to be due to an increase in both TK1 and TK2 levels.