Abstract Objectives To provide improved evidence for treatment recommendations, this study analysed real‐world data on the characteristics, treatment and prognosis of primary extragonadal germ cell tumours (EGCTs), a very rare cancer entity that shares histological features with testicular GCTs (TGCT). Materials and methods This retrospective study analysed data from 34 patients with mediastinal or retroperitoneal EGCTs treated at a high‐volume centre between 2015 and 2025. Probability of overall survival (OS) and relapse‐free survival (RFS) was assessed using Kaplan–Meier curves. Results A primary retroperitoneal and primary mediastinal GCT was diagnosed in 23 (68%) and 11 (32%) patients, respectively. Median patient age was 41.1 years, and 62% were non‐seminomatous in origin. Thirty‐three (97%) patients received chemotherapy according to the IGCCCG prognostic group, and 15 (44%) underwent surgical intervention (4 primary RPLND, 8 post‐chemotherapy RPLND, 3 secondary orchiectomy). Thirteen patients (44.9%) who completed chemotherapy experienced a relapse after a median of 0.79 years, and six of them died. In patients with primary mediastinal seminoma, 3‐year RFS and OS were 100% as compared to 71% 3‐year OS in patients with primary retroperitoneal non‐seminoma and 46% 3‐year RFS in patients with primary mediastinal non‐seminoma. Conclusion The prognosis for primary mediastinal seminoma appears favourable, while non‐seminomatous EGCT shows poorer outcomes. Additionally, primary retroperitoneal seminomas demonstrate promising survival rates, whereas primary retroperitoneal non‐seminomas demonstrate the lowest OS rates.
Kidess et al. (Wed,) studied this question.