Supplementary Material for: Teratomatous Elements in Orchiectomy Specimens Are Associated with a Reduced Relapse-Free Survival in Metastasized Testicular Germ Cell Tumors

<b><i>Introduction:</i></b> The impact of teratomatous elements in orchiectomy specimens of metastasized testicular germ cell tumors (TGCT) regarding oncological outcome is still unclear. <b><i>Methods:</i></b> We performed a retrospective analysis including 146 patients with metastasized TGCT analysing patient characteristics. <b><i>Results:</i></b> Twenty-six (18%) of all patients showed teratomatous elements in the orchiectomy specimens. TGCT with teratomatous elements showed a significantly higher frequency of clinical-stage 2C-3 disease (73 vs. 49%, <i>p</i> = 0.031), visceral metastases (58 vs. 32%, <i>p</i> = 0.015), and poor prognosis (<i>p</i> = 0.011) than TGCT without teratomatous elements. Teratoma-containing TGCT revealed a significantly higher rate of post-chemotherapy retroperitoneal lymph node dissection (PC-RPLND, 54 vs. 32%, <i>p</i> = 0.041), with teratomatous elements being more often present in the PC-RPLND specimens (43 vs. 11%, <i>p</i> = 0.020) than nonteratoma-containing primaries. In the Kaplan-Meier estimates, the presence of teratomatous elements in orchiectomy specimens was associated with a significantly reduced relapse-free survival (RFS) (<i>p</i> = 0.049) during a median follow-up of 36 months (10–115.5). <b><i>Conclusions:</i></b> The presence of teratomatous elements in orchiectomy specimens is associated with an advanced tumor stage, worse treatment response as well as a reduced RFS in metastasized TGCT. Consequently, the presence of teratomatous elements might act as a reliable stratification tool for treatment decision in TGCT patients.