Outcomes of patients with solitary plasmacytomas (SP) in the era of PET imaging and serum-free light chain (sFLC) testing: A single institution experience.

Abstract

8608 Background: SP can occur in bone (SPB) or in extramedullary sites (EMP) and generally accounts for ~ 3-5% of plasma cell dyscrasias. Up to 50% of SPB and 15% of EMP will progress to multiple myeloma (MM). We evaluated the utility and prognostic significance of positron emission tomography (PET) imaging and SFLC ratio (sFLCr). Methods: We retrospectively reviewed electronic medical records of patients with SP evaluated at Moffitt Cancer Center between 1990-2012. The diagnosis of SP was per IMWG criteria (BJH 2003, 121:749) (biopsy proven single site, negative skeletal survey, bone marrow biopsy with no more than 10% plasma cells). Initial and post therapy sFLCr as well as PET findings were correlated with progression to symptomatic MM (PFS). Radiation therapy (XRT) was at the discretion of the treating physician. Results: 135 patients were identified and 91 (67%) were males. The median age was 58 years (range 20-82). Consistent with prior reports, the PFS of the entire cohort was 43 months (95% CI 17.8-70). 23 patients had PET prior to progression. All patients had uptake in the primary lesion (except 4 who had resection of the primary). 8 patients had additional PET findings in other bony structure (PET+), and 15 did not (PET-). 2 and 6 of the PET- and PET+ patients progressed (median PFS Not reached (NR) vs. 8.1 months, p=0.021) respectively. Of the 49 patients with available sFLC data, 32 had an abnormal ratio (17 progressed) and 17 patients had a normal ratio (2 progressed). Abnormal baseline sFLCr was associated with progression (median PFS 19 months vs NR, p=0.012). Post XRT, 44 patients had an available sFLCr, of which 23 had an abnormal ratio and 21 a normal ratio. A persistent serum/urine m spike after XRT was associated with progression to MM (median PFS 20.8 months vs NR, p<0.0001). However, the association between Post XRT sFLCr and progression to MM was not statistically significant (median PFS 19 vs 43 months (abnormal vs normal ratio) p=0.2). Conclusions: PET imaging and sFLC are predictors of outcomes in SP and their routine inclusion in the diagnostic work up of patients with SP will result in a stage migration where patients outcomes are improved compared to historical controls.