Synthesis and metabolism of Bence Jones protein and calculation of tumour burden in patients with Bence Jones myeloma.

Synthesis and metabolism of Bence Jones protein was measured in seven patients with Bence Jones myeloma. Using the plasma and urine levels of 125I-labelled Bence Jones protein, it was possible to calculate the fractional catabolic rate (FCR), fractional proteinuric rate (FPR), and fractional metabolic rate (FMR) for the individual patients. There was a high degree of correlation between decreased metabolism and reduced creatinine clearance (P < 0.001). Ideal regression equations (linear and nonlinear) relating FCR, FPR and FMR with fractional creatinine clearance (FCC) were calculated. Using these regression equations plus measured values for the synthetic rates of light chain for bone marrow plasma cells, the myeloma cell mass or tumour burden was measured in each patient. Correlations between these measured cell mass values and those derived from clinical staging were reasonably good. However, for the lambda (gamma) Bence Jones myeloma patients, the measured cell mass values were significantly higher than predicted from clinical staging. Further studies will be necessary to validate this latter observation. It is hoped that this study will serve as a basis for a comprehensive schema allowing accurate cell mass measurement and staging of Bence Jones myeloma.