Early Recurrence of Mediastinal Germ Cell Tumor With Pathological Complete Response to Chemotherapy: A Case Report

Primary malignant mediastinal germ cell tumors (GCTs) are rare pediatric tumors that have a poorer prognosis than GCTs occurring elsewhere in the body. Due to their rarity and aggressiveness, they are often locally advanced and unresectable at diagnosis, and currently, there is no standard optimal treatment approach. Herein, we present a rare case of pediatric anterior mediastinal yolk sac tumor (YST) diagnosed as pathological complete response (CR) to chemotherapy but prematurely required pulmonary metastasectomy of mixed GCT consisting of seminoma and YST. Testicular GCTs can relapse as tumors of subtypes that are pathologically different from the primary tumor, each having distinct pathogenesis, treatment modality, and prognosis; however, this phenomenon is seldom reported in mediastinal GCTs. This report reviewed the discordance of histological composition between primary and metastatic tumors. When treating mediastinal nonseminomatous GCTs, the possibility of early recurrence should be considered, even if the primary tumor is completely resected and diagnosed as pathological CR to chemotherapy.