Serum thymidine kinase in monoclonal gammopathies. A prospective study. The Cooperative Group for Study and Treatment of Multiple Myeloma.

Between January 1986 and March 1990, the serum levels of thymidine kinase (TK) were evaluated at diagnosis in 97 patients with monoclonal gammopathy of undetermined significance (MGUS) and 149 patients with multiple myeloma (MM) enrolled in a prospective protocol for treatment of MM. At presentation, patients with MGUS had lower TK levels than those with Stage I MM (P less than 0.05) and the overall population of those with MM (P less than 0.0005). TK levels were increased in advanced stages in comparison with earlier ones (P less than 0.01). The TK level was related to survival. With a median follow-up of 29 months, patients with TK levels greater than 7.0 U/microliters had shorter survival times than those with lower levels (medians, 23 and 42 months; P less than 0.0001). In a multivariate analysis, TK explained most of the variability of survival (P less than 0.0001), the remaining being accounted for by serum creatinine and beta-2 microglobulin. No changes in TK levels occurred during follow-up of patients with stable MGUS, whereas TK levels increased in two patients at time of progression to overt MM. In patients with MM, TK levels decreased (P less than 0.01) in those who responded to treatment but increased in those having relapses (P less than 0.03) and those with progressive disease (P less than 0.03). These results indicate that TK has clinical and prognostic relevance in monoclonal gammopathies, and additional investigations are warranted to determine whether it is a useful tool for the clinical evaluation, staging, and follow-up of patients with MM.