PREDICTION OF RESIDUAL RETROPERITONEAL MASS HISTOLOGY AFTER CHEMOTHERAPY FOR METASTATIC NONSEMINOMATOUS GERM-CELL TUMOR - MULTIVARIATE-ANALYSIS OF INDIVIDUAL PATIENT DATA FROM 6 STUDY-GROUPS

Purpose: To develop a statistical model that predicts the histology (n ecrosis, mature teratoma, or cancer) after chemotherapy for metastatic nonseminomatous germ cell tumor (NSGCT). Patients and Methods: An int ernational data was collected comprising individual patient data from six study groups. Logistic regression analysis was used to estimate th e probability of necrosis and the ratio of cancer and mature teratoma. Results: Of 556 patients, 250 (45%) had necrosis at resection, 236 (4 2%) had mature teratoma, and 70 (13%) had cancer. Predictors of necros is were the absence fo teratoma elements in the primary tumor, prechem otherapy normal alfa-fetoprotein (AFP), normal human chorionic gonadot ropin (HCG), and elevated lactate dehydrogenase (LDH) levels, a small prechemotherapy or postchemotherapy mass, and a large shrinkage of the mass during chemotherapy. Multivariate combination of predictors yiel ded reliable models (goodness-of-fit tests, P > .20), which discrimina ted necrosis well from other histologies (area under the receiver oper ating characteristics (ROC) curve, .84), but which discriminated cance r only reasonably from mature teratoma (area, .66). Internal and exter nal validation confirmed these findings. Conclusion: The validated mod els estimated with high accuracy the histology at resection, especiall y necrosis, based on well-known and readily available predictors. The predicted probabilities may help to chose between immediate resection of a residual mass or follow-up, taking into account the expected bene fits and risks of resection, feasibility of frequent follow-up, the fo llow-up, the financial costs, and the patient's individual preferences .