Progression in solitary plasmacytoma of bone: impact of occult marrow disease (OMD) and urinary light chains (ULC) on outcome. (A) OMD was demonstrable in 34 of 50 (68%) patients and was associated with an inferior outcome. Progression was documented in 72% (26/34) of patients with OMD compared with 12.5% (2/16) without. The median time to progression (TTP) was 26 months vs not reached, respectively (P = .003). (B) The presence of ULC was also associated with an inferior outcome because progression was documented in 91% (10/11) with ULC and 44% (15/34) without. The median TTP was 16 vs 82 months, respectively (P < .001). (C) When both parameters are assessed, patients may be defined as high risk by the presence of OMD and/or ULC (75% [24/32] progression), and they may be defined as low risk by the absence of both parameters (7.7% [1/13] progression). Median TTP was 23 months vs NR (P = .001).