Misuse of tumor marker levels leads to an insufficient International Germ Cell Consensus Classification (IGCCCG) risk group assignment and impaired treatment.

Background: Metastatic germ cell tumors of the testis (GCTs) are risk-stratified according to the International Germ Cell Cancer Collaborative Group (IGCCCG) classification system. This risk classification is based on anatomical risk factors as well as tumor marker levels of AFP, HCG, and LDH assessed pre-chemotherapy after orchiectomy treatment. An incorrect classification is possible when pre-orchiectomy marker levels are used, possibly resulting in over- or undertreatment of patients. The aim was to investigate the potential frequency and clinical relevance of incorrect risk stratification using pre-orchiectomy tumor marker levels.

Methods: A multicenter registry analysis, including patients with metastasized nonseminomatous GCT (NSGCT), was conducted by investigators of the German Testicular Cancer Study Group (GTCSG). Based on the marker levels at different timepoints, IGCCCG risk groups were calculated. The agreement was tested using Cohen's kappa.

Results: A total of 672 of 1910 (35%) patients were diagnosed with metastatic NSGCTs, and 523 (78%) had sufficient data for 224 follow-up data points. By using pre-orchiectomy tumor marker levels, 106 patients (20%) would have been incorrectly classified. Seventy-two patients (14%) were classified into a higher risk category, and 34 patients (7%) were classified into a lower risk category. Cohen's kappa was 0.69 (p < 0.001), showing a strong agreement between the use of both marker timepoints. The treatment of misclassified patients would have resulted in an overtreatment of 72 patients or undertreatment of 34 patients.

Conclusions: The use of pre-orchiectomy tumor marker levels may lead to an incorrect risk classification and might subsequently lead to under- or overtreatment of patients.