Primary gastric mixed germ cell tumor in an infant: the pivotal role of dynamic alpha-fetoprotein surveillance in unmasking occult malignancy.

This paper reports a case of an extremely rare primary mixed germ cell tumor (MGCT) of the stomach in an infant. The patient, an 8-month-old male infant, presented with “black stool for three days.” Abdominal computed tomography (CT) suggested an abdominal space-occupying lesion, and gastroscopy revealed a huge cauliflower-like protrusion on the lesser curvature of the gastric body. The patient first underwent exploratory laparotomy for biopsy and adhesiolysis, followed by open resection of the abdominal mass with gastric wall repair, pyloroplasty, and abdominal drainage. Postoperative pathology suggested an immature teratoma (Grade I). After the initial surgery, although the pathological diagnosis was immature teratoma, serial AFP monitoring revealed persistently elevated levels that further increased significantly (from 465.8 ng/mL to over 1000 ng/mL within one week). Concurrent follow-up CT suggested a space-occupying lesion in the original tumor bed. The second laparotomy was performed for residual lesion in the original tumor bed combined with adhesiolysis and abdominal drainage, with the intent of achieving radical resection. Pathology confirmed MGCT (95% immature teratoma and 5% yolk sac tumor). The patient then received four cycles of alternating Vincristine + Cyclophosphamide + Cisplatin/Isocyclophosphamide + Etoposide + Vincristine (VCP/IEV) chemotherapy, after which AFP normalized. As of the last follow-up (August 2025), the patient has been disease-free for over 48 months and is in good general condition.