Tumor burden in Hodgkin's lymphoma can be reliably estimated from a few staging parameters

Abstract
The relative tumor burden (rTB), the tumor burden normalized to body surface area, is of prime clinical and prognostic value in Hodgkin's lymphoma. However, its measurement is rather complicated and a bedside computation cannot be proposed. We investigated the possibility of estimating, instead of measuring, rTB from elementary parameters of the initial staging. The rTB of 507 patients, treated with therapeutic protocols of the Gruppo Italiano Studio Linfomi according to their staging characteristics, was measured through their pre-therapy computed tomographies. The relationships between rTB and staging characteristics were analyzed with simple and multiple regressions both in a training sample (254 patients) for a selection of predictive parameters, and in a test sample (253 patients) for validation of the results. The number of involved sites, bulky mass and the IPI score were the variables best related to rTB. The resulting final equation {estimated rTB=-4.3+8.3xIPI2+22.7x[no. of involved sites (+3 if a bulky mass is present)]} provided the maximal approximation to the measured rTB (R2=0.671). The validity of the equation was confirmed on the test sample and the predictive superiority of the estimated rTB over IPI was still evident in terms of failure-free survival in both groups of patients. The estimated rTB is accurate enough to retain most of the prognostic advantage of the measured rTB over the IPI score. It can be easily calculated, allows a valid approximation of the measured rTB, and can be proposed as a useful tool for clinical research and practice.