An Ultra-late Recurrence with Adenoid Cystic Carcinoma-like Malignant Transformation of a Pineal Immature Teratoma after 35 Years: A Case Report

Immature teratomas of the pineal region are a subtype of non-germinomatous germ cell tumors typically associated with early recurrence. Ultra-late recurrence decades after initial treatment is exceedingly uncommon. We report an immature teratoma case in the pineal region that recurred 35 years after subtotal resection and chemoradiotherapy, showing somatic-type malignant transformation into adenoid cystic carcinoma-like adenocarcinoma. A 16-year-old boy initially underwent ventriculoperitoneal shunting followed by tumor resection, after the pathological confirmation of an immature teratoma (grade 2 according to the ovarian teratoma grading system). A small residual lesion remained, and the patient's condition remained stable for more than a decade, but he was lost to follow-up. At 51 years of age, the patient presented with obstructive hydrocephalus and tumor regrowth. Preoperative serum and cerebrospinal fluid tumor markers levels were normal. An endoscopic biopsy revealed poorly differentiated adenocarcinoma. Resection through an occipital transtentorial approach indicated tumor infiltration into the bilateral thalamus. Histology showed glandular and cartilaginous components with marked atypia and immunohistochemical features resembling adenoid cystic carcinoma, whereas germ cell markers were negative, thus establishing a diagnosis of teratoma with somatic-type malignant transformation. Despite ifosfamide, carboplatin, and etoposide chemotherapy (all at 50% dose) and stereotactic radiosurgery, the disease progressed with leptomeningeal dissemination, and the patient died 613 days after he underwent the second surgery. This case represents the longest reported interval of recurrence for a central nervous system immature teratoma and highlights the possibility of long-term tumor dormancy followed by malignant transformation. Lifelong surveillance is therefore warranted in patients with residual immature teratomas.