Validation of clinical prognostic indices for diffuse large B-cell lymphoma in the National Cancer Data Base

Accurate risk stratification is necessary for epidemiologic and outcomes research in diffuse large B-cell lymphoma (DLBCL). We evaluated performance characteristics of the clinically derived International Prognostic Index (IPI) and revised IPI (R-IPI) with a regression model-based score using the National Cancer Data Base.

We studied DLBCL patients diagnosed in 2004-2011, divided into derivation and validation cohorts. The model-based score was calculated from a Cox model incorporating variables routinely recorded by cancer registries. Calibration and discrimination of the indices with regard to overall survival were evaluated in the validation cohort.

The IPI was recorded in 19,511 of 119,942 patients, of whom 79 % received chemotherapy. Both clinical indices provided good survival discrimination (5-year estimate range 33-74 % for the IPI, and 41-87 % for the R-IPI), but explained only 16 % of variation in survival. Survival predictions among chemotherapy-treated patients were similar to estimates from published clinical cohorts. The model-based score had significantly better discrimination characteristics (5-year survival estimate range 22-87 %) and explained 23 % of variation in survival.

We validated the IPI and R-IPI as recorded by cancer registries to provide robust risk stratification in the general population with DLBCL, but a prognostic model using raw registry data provides superior performance. Explicit recording of prognostic factors is preferable to abstracting coarsened clinical indices for the purpose of population-based epidemiologic research. Considering low variation of survival explained by the standard clinical variables, incorporating molecular markers into registry data is necessary to improve risk stratification.