There is some data to support the use of sFLC analysis to monitor patients with SBP. Leleu et al.  monitored 10 patients and observed a trend to shorter time to progression (to MM) in patients with no change in sFLCs following radiotherapy. The same group  also described a patient with monoclonal κFLC in whom sFLCs were abnormal at disease relapse while electrophoresis and MRI were both ‘unremarkable’. A subsequent MRI investigation and biopsy confirmed relapse 6 months later, whilst serum and urine electrophoresis results remained normal.
National Comprehensive Cancer Network® (NCCN®) guidelines recommened sFLC analysis alongside serum protein electrophoresis (SPE) and serum IFE in a panel of tests for surveillance/follow-up of solitary plasmacytoma after primary treatment (Section 25.8) .