Mesonephric-like adenocarcinoma of the ovary: features of a rare and aggressive entity associated with endometriosis.

Objective: Mesonephric-like adenocarcinoma is a rare, aggressive ovarian cancer subtype, newly classified by the World Health Organization in 2020. This study examines the clinical, ultrasound, pathological features, and survival outcomes of ovarian mesonephric-like adenocarcinoma.

Methods: This observational, prospective, single-center study included patients with ovarian mesonephric-like adenocarcinoma treated between January 2020 and December 2023. Clinical data and ultrasound findings were collected. Ultrasound examinations were performed according to the International Ovarian Tumor Analysis guidelines and qualitatively described in correlation with pathological findings. Histopathological evaluation was conducted based on the 2020 World Health Organization classification. Progression-free survival and overall survival were calculated from the time of diagnosis to recurrence or death.

Results: Among 467 patients with ovarian cancer treated at our center, 14 (3.0%) were diagnosed with ovarian mesonephric-like adenocarcinoma, with a mean age of 60 ± 8 years. Ultrasound commonly showed unilateral solid lesions (57.2%) with moderate-to-strong blood flow, heterogeneous echogenicity, and hyperechoic "cotton candy" regions. Most patients (57.1%) had International Federation of Gynecology and Obstetrics stage III to IV disease; 78.5% underwent upfront surgery, achieving complete cytoreduction in 92.8%. Pathology revealed mesonephric-like adenocarcinoma alone in 44.4% and mixed histotypes in 55.6% (endometrioid, mucinous, or high-grade serous components), with endometriosis in 64.2%. K-RAS mutations were present in all cases. Median progression-free survival was 17.5 months (IQR 13.5-35.9), with 57.1% experiencing recurrence, mostly as peritoneal metastases. Median overall survival was not reached, with one death recorded.

Conclusions: Mesonephric-like adenocarcinoma is a rare yet aggressive ovarian cancer strongly associated with endometriosis and characterized by K-RAS mutation. Unique ultrasound features, such as "cotton candy" hyperechoic regions, may assist in early recognition and pre-surgical diagnosis.