Evaluation of serum deoxythymidine kinase as a marker in multiple myeloma

A recently developed deoxythymidine kinase assay utilizing 125I-iododeoxyuridine as substrate was used in an investigation of sera from 122 untreated patients with multiple myeloma. Most patients had slightly elevated or normal serum deoxythymidine kinase activity (S-TK), although in some patients values increased by more than forty-fold were found. S-TK correlated with the haemoglobin level but did not correlate with sex, age, erythrocyte sedimentation rate, nor with the serum concentrations of creatinine, beta 2-micro-globulin, Ca or M-component. The distribution of S-TK values in IgG, IgA and pure Bence-Jones myeloma did not differ significantly. Patients with IgG and IgA myeloma excreting light-chain immunoglobulin in the urine had significantly higher S-TK than non-excreters. There was a significant correlation between S-TK values and tumour cell mass as determined by clinical staging. A high pretreatment S-TK (greater than 5.1 units) also distinguished a group of patients with a significantly shorter survival time. Patients with no response to initial therapy had significantly higher S-TK values than those who did respond. In longitudinal studies of 11 patients, S-TK was found to increase when the disease became more aggressive. The possibility of diagnosing disease progression at an early stage by an elevation of S-TK is discussed.