Validation of a prediction model and its predictors for the histology of residual masses in nonseminomatous testicular cancer

Purpose: We validated a prediction model for histology of residual retroper itoneal masses, either benign or tumor, in patients treated with chemothera py for metastatic nonseminomatous testicular cancer. Materials and Methods: We studied 276 patients treated with chemotherapy be fore retroperitoneal lymph node dissection at Indiana University Medical Ce nter between 1985 and 1999. A previously developed prediction model was mod ified to provide predictions for the Indiana population based on 5 predicto rs. For these predictors, including teratomatous elements in the primary tu mor, pre-chemotherapy tumor markers (alpha -fetoprotein and human chorionic gonadotropin), size of the residual mass and reduction in mass size, univa riate and multivariate odds ratios were determined. The modified model was evaluated by calculating the concordance statistic and studying model relia bility. Results: All odds ratios from univariate and multivariate analyses were in the expected directions. The modified model had good discriminative ability (concordance statistic 0.79). However, the predicted probabilities for ben ign tissue were generally too high due to the low prevalence of benign tiss ue (76 of 276 cases or 28%). Conclusions: This study confirms the predictive ability of formerly identif ied predictors for the histology of residual retroperitoneal masses in test icular cancer. However, the previously developed prognostic model must be a djusted for the local overall ratio of benign versus tumor histology to pro vide reliable predictions in the Indiana population.