Divergent Biology and Outcomes of Somatic Transformations in Germ Cell Tumors

PURPOSE: Somatic-type malignancy (SM) of germ cell tumor (GCT) is rare but demonstrates aggressive behavior. Differences by primary site, time to transformation, and mutational status remains poorly characterized. PATIENTS AND METHODS: We reviewed all SM patients from June 2016 - May 2025 at a tertiary referral center. Time to somatic transformation (TST) was defined from initial GCT diagnosis to SM detection. SM were classified based on time of detection- at initial diagnosis (de novo), at consolidative surgery, relapse under 5 years, and evolved SM- relapse after 5 years. Descriptive statistics, Kaplan-Meier estimates, and Cox regression analyses were used. RESULTS: 72 patients were identified: 40 (56%) with testicular, 24 (33%) with mediastinal, and 8 (11%) with other primaries. 22/24 (92%) mediastinal tumors with SM had sarcomatous transformation. Sarcoma was seen in 25/42 (60%) of de novo SM while adenocarcinoma was detected as an evolved entity in 5/6 (83.3%) cases. Embryonic type neuroectodermal tumor (ENET) histology carried poor prognosis compared to non-ENET histology (median OS 1.8 vs 8 years; HR 1.94, p = 0.1). Genomic data available showed PTEN-AKT-mTOR pathway mutations (33%) and TP53 mutations (33%), enriched in extra-gonadal sarcomatous SM. CONCLUSIONS: SM exhibits temporal, histologic, and molecular distinctions across primary sites. Response to front-line therapy and survival outcomes are poor. Future direction includes the exploration of underlying predictors of transformation and identification of targetable alterations in the relapsed setting.