Will sFLC concentrations help in understanding tumour kinetics?
This is an important issue. At present, intact monoclonal immunoglobulins in serum or FLCs in urine are used to monitor the progress of patients. The half-life of IgG is 3-4 weeks, so reductions in tumour mass with chemotherapy may not be reflected in serum monoclonal protein changes for several weeks. The half-life of FLCs is only a few hours – extending to 2-3 days when renal function is impaired. Thus, reductions in tumour mass with chemotherapy can be identified earlier when the patients are being monitored using sFLC tests. Indeed, changes in tumour mass might be assessed between each cycle of chemotherapy allowing subsequent treatments to be specifically tailored to individual patients. Changes in urine and serum levels of FLCs broadly correspond but renal tubular reabsorption prevents accurate assessment of tumour responses from urine measurements. Approximately 95% of patients with MM, excreting intact immunoglobulins haveabnormal sFLCs. It is likely, because of the short half-
