Abstract
We describe a rare and remarkable transformation of an immature mediastinal teratoma into high-grade angiosarcoma in a 21-year-old male. Mediastinal teratomas, particularly immature ones, are exceedingly rare, representing a small fraction of germ cell tumors (GCTs). Our case describes the clinical journey of the patient, who initially presented with acute chest pain and was subsequently diagnosed with an immature teratoma following imaging studies and elevated tumor markers. Despite an initial positive response to cisplatin-based chemotherapy, surveillance imaging revealed liver masses, which a biopsy confirmed as angiosarcoma. This transformation underscores the aggressive nature of immature teratomas and the propensity for sarcomatous differentiation, particularly in the mediastinum. The case contributes valuable insight into the management and surveillance of mediastinal non-seminoma germ cell tumors (MNGCT), a subset of GCTs with limited literature. We believe this case is the first in the literature to describe a transformation from an immature teratoma in the mediastinum to a high-grade angiosarcoma.