DOI: https://doi.org/10.36347/sjmcr.2026.v14i03.019

Pages: 401-405

Immature ovarian teratomas are rare malignant germ cell tumors that typically occur in young women and have a favorable prognosis when treated with surgery and adjuvant chemotherapy. However, late recurrence with somatic-type malignant transformation is extremely uncommon. We report the case of a 48-year-old woman previously treated in 2002 for a FIGO stage IC2, grade 3 immature ovarian teratoma with left adnexectomy followed by four cycles of BEP chemotherapy. After a 20-year disease-free interval, the patient presented in 2022 with a hard parietal mass. Imaging and biopsy revealed an invasive mucinous adenocarcinoma of probable digestive origin. She received XELOX chemotherapy with partial response and underwent complete surgical resection. Histological analysis confirmed a low-grade mucinous tumor arising within a mature teratoma, consistent with a somatic-type malignancy. In 2024, the patient developed a large abdominopelvic mass with peritoneal involvement. Surgery revealed a mucinous carcinoma with signet-ring cells and peritoneal carcinomatosis. Molecular analysis showed an NRAS G12S mutation. She was started on palliative chemotherapy with FOLFIRI and bevacizumab. This case highlights a rare example of late relapse of an immature ovarian teratoma with transformation into mucinous adenocarcinoma of gastrointestinal phenotype. It underscores the importance of long-term surveillance and the role of immunohistochemistry and molecular profiling in guiding diagnosis and treatment.