Mucinous adenocarcinoma in a young female: A case report of unusual-origin low-grade neoplasm presenting as retroperitoneal mass

Introduction: Mucinous adenocarcinoma of the ovary is an uncommon type of epithelial ovarian cancer that predominantly occurs in women between their fourth and sixth decades of life. Presentation in younger women with atypical features, such as retroperitoneal cystic masses, is rare and will tend to delay diagnosis. Case Report: After two caesarean sections, a 33-year-old multiparous woman (G2P2L2A0) experienced one to two months of right lower abdominal pain and swelling. A huge, multiloculated abdominopelvic cystic lesion on the right side was revealed by an imaging. The tumor was removed by laparoscopic surgery. Gross pathology showed an ovarian cyst with smooth walls measuring 22 × 14 × 10 cm. A mucinous cystadenoma was initially intimated by histopathological examination, but later examination and immunohistochemistry presented features consistent with a low-grade mucinous adenocarcinoma of probable ovarian origin. Immunostaining for PAX-8, WT-1, and CDX2 was negative, while that for CK7 and CA-125 was positive. In the absence of any suggestion of distant metastasis, postoperative positron emission tomography-computed tomography (PET-CT) demonstrated a moderately FDG-avid cystic mass in the right adnexa, suggesting persistent disease. Conclusion: This case highlights the importance of an exhaustive immunohistochemical and histological evaluation in young women presenting with complex pelvic tumors. Mucinous adenocarcinoma should be identified at an early stage to guide treatment and improve prognosis. For optimal management, an imaging-based multidisciplinary approach with surgery and oncologic consultation is required.