A number of groups have identified prognostic factors that are associated with inferior disease-free survival and progression to MM. These include tumour location and size , presence of a monoclonal protein at diagnosis , and levels of uninvolved immunoglobulins . In addition, bone marrow plasmacytosis  and the persistence of a serum monoclonal protein after treatment  have both been consistently associated with inferior progression-free survival (PFS). However, as persistence of a monoclonal protein can only be assessed 1 or 2 years after initiation of therapy, there is a clear need for alternate reliable prognostic markers that can be measured at diagnosis .. During follow-up, a total of 43/116 patients progressed to MM with a median time to progression of 1.8 years. Patients with an abnormal κ/λ sFLC ratio had an increased risk of progression compared to those with a normal ratio (44% vs. 26% at 5 years, p=0.039) (Figure 21.2). Patients with an abnormal κ/λ sFLC ratio at diagnosis also had a shorter overall survival (Figure 21.3). Persistence of a serum monoclonal immunoglobulin (≥5 g/L) after 1-2 years of therapy was an additional risk factor for progression to MM. A risk stratification model was constructed based on these two risk factors, which defined low-, intermediate- and high-risk groups with 0, 1 or 2 risk factors, and with 5-year progression rates of 13%, 26% and 62%, respectively (Figure 21.4). The authors commented that sFLC analysis provided important prognostic information in solitary plasmacytoma. A subsequent study by Koch et al.  confirmed the prognostic value of baseline sFLC ratio measurements.  assessed the prognostic utility of sFLCs and whole body fluorodeoxyglucose positron emission tomography – computed tomography (FDG-PET CT) in 43 patients with solitary plasmacytoma (33 SBP and 10 EMP). By univariate analysis, an abnormal iFLC concentration, an abnormal κ/λ sFLC ratio or the presence of ≥2 hypermetabolic lesions on initial PET CT were associated with significantly shorter time to MM progression (Figure 21.5, p=0.002; and data not shown). On multivariate analysis, an abnormal iFLC concentration and the presence of ≥2 hypermetabolic lesions on PET-CT were the strongest independent prognostic factors identifying patients at greatest risk of progression to MM. A risk stratification model based on the presence of 0, 1, or 2 risk factors demonstrated that the median time to progression to MM for each group was “Not reached”, 41 and 21 months, respectively (Figure 21.6).