Background: Malignant Brenner tumor (MBT) is an exceptionally rare epithelial ovarian neoplasm, accounting for less than 1% of malignant ovarian tumors. No prospective data exist, and systemic therapy is extrapolated from high-grade epithelial ovarian carcinoma. Case presentation: A 37-year-old woman presented with abdominal pain, bloating and altered bowel habit. CT showed a large sigmoid mass inseparable from the left ovary and multiple hepatic lesions; CA-125 was 797 U/mL. Image-guided liver biopsy showed poorly differentiated adenocarcinoma, and sigmoid biopsy showed undifferentiated carcinoma expressing p63 and GATA3, consistent with MBT of ovarian origin (FIGO stage IVB). After multidisciplinary review, palliative carboplatin (AUC 5) and paclitaxel (175 mg/m²) every 21 days were started. Nine days after cycle 2 she developed febrile neutropenia (ANC 0.22 × 10⁹/L) with hypotension and a lactate of 10 mmol/L, requiring 24 hours of intensive care; cultures were negative and she recovered with piperacillin–tazobactam and fluid resuscitation. Treatment resumed at reduced doses (carboplatin AUC 4, paclitaxel 150 mg/m²) with pegfilgrastim. CA-125 rose to 1,232 U/mL before cycle 2 and fell to 645 U/mL before cycle 3; CT after cycle 2 showed stable hepatic metastases and a mild response of the pelvic primary. Literature update: Following the PRISMA-based 2024 systematic review (115 cases, searched to 15 September 2023), a provisional update search identified four further patients with ovarian MBT meeting the review's diagnostic criteria, with five more awaiting full-text assessment. All included cases, and all pending cases with a reported stage, were stage I–II; none described stage IV disease or hepatic metastases. Conclusions: Diagnosing MBT on biopsy material alone is difficult and depends on integrating morphology and immunohistochemistry with exclusion of urothelial and colorectal primaries. Treatment evidence is limited to case reports, small series and registry data, and carboplatin–paclitaxel is the most commonly reported regimen. Genomic data suggest that MBT is usually microsatellite-stable without homologous recombination deficiency and frequently carries FGFR3 alterations, so comprehensive profiling is more informative than empirical PARP or checkpoint inhibition.