Serum thymidine kinase and beta-2 microglobulin in monoclonal gammopathies.

We evaluated the serum thymidine kinase (TK) and beta-2 microglobulin (beta-2) levels of 22 patients with monoclonal gammopathy of undetermined significance (MGUS) and of 29 patients with multiple myeloma (MM). Both parameters were significantly lower in MGUS than in MM patients and in early (stage I + II) than in advanced (stage III) MM. TK was also lower in MGUS than in stage I MM (p less than 0.025). A seven-fold increase of TK level was documented in one patient who developed a full blown picture of MM 6 years after a diagnosis of MGUS. In 3 patients with stage III MM, a sharp decrease in TK (40-77%) and in beta-2 (29-53%) levels at remission was evident with respect to the levels measured at diagnosis. Patients with high levels of TK or beta-2 had a shorter survival than those with low levels; however, this was statistically significant only for beta-2 levels (p less than 0.02). Serum TK as well as beta-2 levels appear to be of clinical value in monoclonal gammopathies and related to the course of the disease.