SIL index, comprising stage, soluble interleukin-2 receptor, and lactate dehydrogenase, is a useful prognostic predictor in diffuse large B-cell lymphoma.

Rituximab (R) plus doxorubicin, cyclophosphamide, vincristine, and prednisolone (CHOP) chemotherapy (R-CHOP) is widely accepted as standard care for diffuse large B-cell lymphoma (DLBCL) patients. The revised International Prognostic Index (R-IPI) was established in 2007 after the addition of rituximab to standard DLBCL treatment. To reassess the utility of R-IPI, we carried out a retrospective analysis of patients with DLBCL uniformly treated with standard R-CHOP. Progression-free survival (PFS) curves in "very good" and "good" risk groups as defined by the R-IPI showed no statistical difference. We added soluble interleukin-2 receptor (sIL-2R) level to the factors comprising the R-IPI. Five levels of sIL-2R were weighed with respect to their impact on PFS. sIL-2R of >2500 U/mL was determined as the most appropriate threshold. We developed a new prognostic SIL index, which includes three independent prognostic risk factors: clinical stage (S); sIL-2R level over 2500 U/mL (I); and elevated lactate dehydrogenase level (L). This index indicates standard risk (0 or 1 risk factors, 4-year PFS 83%, 4-year overall survival 91%) and high risk (2 or 3 risk factors, 4-year PFS 52%, 4-year overall survival 67%) outcomes. The SIL index is a simple and objective prognostic index for DLBCL patients to identify candidates for experimental therapy other than R-CHOP.