EP23.29: Gastric‐type mucinous neoplasia in the ovary: a false negative for ADNEX

Gastric-type mucinous neoplasms of the ovary suppose a diagnostic challenge, as many of their characteristics, such as presence of solid tissue, increased vascular score, and presence of free fluid, are indicators of malignancy. 85-90% of primary tumours are of the intestinal subtype, while 10-15% are of the endocervical, seromucinous, or mixed subtype. The gastric subtype not associated with HPV has shown to have a worse prognosis due to increased distant metastasis, deep stromal invasion, higher stage at presentation, and lower disease-free survival of 30% at 5 years. We present the case of a 43-year-old patient with a history of pharmacological management of endometriosis and laparoscopic right cystectomy 2 months ago. Without other relevant family or gynecological history, a follow-up transvaginal pelvic ultrasound revealed a multilocular cystic mass in the right adnexa with punctate echogenic images inside one of its locules, with low malignancy risk (O-RADS 3) and 97.8% benignity according to IOTA Adnex. The patient underwent laparoscopic hysterectomy and bilateral salpingectomy. Histology revealed a mucinous neoplasm in the right ovary with epithelium resembling cervical adenocarcinoma associated with endometriosis, positive for CD31 and D2-40, with no evidence of lymphovascular invasion. Additionally, an infiltrating endocervical adenocarcinoma not associated with HPV, of well-differentiated gastric type, stage IB2-3, was found, indicating management by oncology and gynecologic oncology, who determined chemotherapy with cisplatin, radiotherapy, and brachytherapy. In the context of post-surgical follow-up in patients, it is valuable to identify atypical cases of recurrent adnexal lesions as they could lead to invasive non-ovarian origin pathologies.