Metastatic Patterns of Malignant Germ Cell Tumors Vary by Histologic Subtype and Primary Site

Background and Objectives: Malignant germ cell tumors (GCTs) are rare but clinically significant neoplasms arising in gonadal and extragonadal sites. Malignant GCTs, divided into seminomatous and non-seminomatous subtypes, show diverse biological behavior. Although molecular studies have advanced understanding of their origins and genetic features, little is known about metastatic patterns due to their rarity and generally favorable outcomes. This study aimed to describe metastatic patterns of malignant GCTs across primary sites and histologic subtypes using population-based database. Materials and Methods: Data were extracted from the Surveillance, Epidemiology, and End Results (SEER) program for patients diagnosed with malignant GCTs between 2010 and 2022. Cases were stratified by primary site (testis, ovary, mediastinum), age group (<8 years vs. ≥8 years), and histologic subtype. Metastatic patterns were assessed using both overall and organotropic metastasis rates, and differences between groups were evaluated descriptively using appropriate statistical tests. Results: A total of 32,015 malignant GCTs were identified, comprising 93.0% testicular, 5.6% ovarian, and 1.4% mediastinal tumors. In patients aged ≥8 years, ovarian tumors tended to show generally lower lymph node and distant metastasis rates. In contrast, mediastinal tumors appeared to have the highest distant metastasis rates. Organotropic analysis suggested distinct subtype- and site-specific differences. For seminoma/dysgerminoma, the organotropic metastasis pattern was generally consistent across different primary sites, whereas the other subtypes showed variable organotropic metastasis rates depending on the primary site. Conclusions: The metastatic patterns of GCTs appear to differ by histologic subtype and primary site. These findings suggest that both subtype and site of origin should be considered when assessing metastatic risk and may provide a framework for improved risk stratification in clinical practice.