Mapping Metastatic Spread in Uterine Sarcoma: A Population-Based Analysis of First Metastatic Patterns and Outcomes

Objective: To characterize the frequency, timing, patterns of first distant metastasis, and post-metastatic survival in uterine sarcoma using population-based registry data. Methods: This study included all patients diagnosed with uterine sarcoma between 2000 and October 2025 in the regional cancer registry of Saxony-Anhalt, Germany. Patients with carcinosarcoma were excluded. Metastatic disease was classified as primary (present at diagnosis or ≤3 months) or metachronous (>3 months). Metastatic patterns were analyzed based on the first metastatic presentation only. Overall survival (OS), recurrence-free survival (RFS), and post-metastatic OS were estimated using Kaplan-Meier methods. RFS was defined as the interval from confirmed tumor-free status after primary therapy to first recurrence or death, and was restricted to patients who achieved tumor-free status (n = 114). Multivariable Cox regression analyses for OS and RFS were performed with administrative censoring at 5 years. Results: A total of 155 patients with uterine sarcoma were included. During follow-up, 54 patients (34.8%) were diagnosed with metastatic disease, of whom 30 (55.6%) presented with primary metastatic disease. Lung was the most frequent site of first metastasis, followed by bone, peritoneum, and liver; 43.4% of metastatic patients had multiple synchronous metastatic sites at first presentation. Median time to first metastasis was short, with several metastatic sites showing median values of zero months, reflecting the high proportion of primary metastatic disease. Median post-metastatic OS was 12 months. Advanced FIGO (Fédération Internationale de Gynécologie et d'Obstétrique) stage and failure to achieve tumor-free status after primary therapy were independently associated with worse OS, whereas histologic subtype was not. Conclusions: In this population-based cohort, metastatic disease occurred in more than one-third of patients with uterine sarcoma and was frequently present at diagnosis. Lung metastases predominated as the first site of distant spread, and post-metastatic survival was poor. These findings underscore the importance of comprehensive staging at diagnosis and highlight the aggressive metastatic behavior of uterine sarcoma in real-world practice.