Recurrence of Primary Mediastinal Yolk Sac Tumor with Brain Metastases: A Case Report and Literature Review.

Primary mediastinal yolk sac tumor (PMYST) is a rare and highly malignant germ cell tumor. We present a 24-year-old male admitted in 2018 with PMYST, superior vena cava syndrome (SVCS), and pulmonary and lymph node metastases. Following chemotherapy and partial resection, brain metastasis occurred; complete remission (CR) was achieved with chemotherapy plus cranial radiotherapy. Multiple bone metastases developed after 6 years. Re-resection revealed adenocarcinoma, consistent with chemotherapy-related malignant transformation. Despite multiple lines of chemotherapy and radiotherapy, the disease progressed, with an overall survival (OS) of 82 months. This case illustrates the complex clinical course of PMYST and the value of dynamic tumor marker and imaging surveillance.