Uncommon Presentation of a Benign Brenner Tumor Mimicking Malignancy: A Case Report.

Background and Aims: Brenner tumor (BT) is a rare ovarian epithelial tumor, with approximately 95% of cases being benign. Because of its rarity and nonspecific clinical radiological features, benign BT may mimic ovarian malignancy. We present a case of a benign BT with clinical, radiological, and intraoperative findings suggestive of malignancy. Method: A 69-year-old postmenopausal woman presented with progressive abdominal enlargement, abdominal pain, and a 10 kg weight loss over 2 months. Ultrasonography showed an ovarian mass with both benign and malignant IOTA features, whereas risk of malignancy index-2 (RMI-2) was 1350. Abdominal laparotomy with total hysterectomy, bilateral salpingo-oophorectomy, and omentectomy was performed. Histopathological examination of the ovarian mass demonstrated features suspicious for MBT, whereas epithelial cell clusters identified in the omental specimen raised concern for metastatic involvement. Immunohistochemical examination showed CK7 and p63 positivity in ovarian tumor but negative expression in omental specimen, excluding metastatic BT. Result: Despite the patient's postmenopausal status, large tumor size, elevated CA-125 level, high RMI-2 score, and intraoperative omental adhesion, the final diagnosis was benign BT. The case demonstrates the potential for benign BTs to mimic advanced ovarian malignancy clinically and radiologically. Immunohistochemistry was particularly useful in resolving the diagnostic uncertainty regarding the suspected omental metastasis. Conclusion: Benign BTs may present with features strongly suggestive of malignancy. Careful histopathological evaluation is essential, and immunohistochemistry can provide valuable diagnostic clarification when metastatic involvement or malignant transformation is suspected.