Endocrine Abstracts

Background: Struma ovarii is a germ cell tumor of the ovary containing ≥ 50% thyroid tissue and malignant struma ovarii (MSO) is a very rare disease containing papillary or follicular thyroid carcinomas (FTC). There is no consensus on optimal management for patients with MSO and no data on radioactive iodine (RAI) responsiveness. Here, we report two cases with RAI refractory MSO with NRAS mutation detected by next-generation sequencing (NGS).

Case 1: A 25-year-old nulligravida patient underwent laparoscopic salpingo-oophorectomy due to a 5.7 cm mass in the left ovary. Pathological examination revealed an MSO (FTC) and additional exploratory laparotomy found multiple metastatic FTC in the peritoneum. She underwent total thyroidectomy and 200 mCi of RAI therapy. There was no RAI uptake in multiple peritoneal nodules on post-therapeutic whole-body scan (WBS) and her stimulated serum thyroglobulin (Tg) level was 826 ng/mL NGS analysis identified NRAS Q16K mutation.

Case 2: A 44-year-old patient (gravida 2) underwent laparoscopic right ovarian cystectomy for a 10.5 cm mass. The pathology was poorly differentiated thyroid carcinoma arising in MSO and she underwent a hysterectomy and bilateral salpingo-oophorectomy. The pathology confirmed the residual MSO without invasion of adjuvant tissues. Adjuvant RAI therapy (150mCi) was done after total thyroidectomy of the normal thyroid gland and there was no abnormal RAI uptake in the pelvic cavity. Eight months later, peritoneal seeding of MSO was detected in FDG-PET scan with serum Tg increase from 31.6 ng to 66.5 ng/mL RAI refractoriness was confirmed after an additional 200 mCi of RAI therapy. She underwent additional surgery for the increase of peritoneal mass with colon invasion. NRAS Q16K mutation was also confirmed by NGS analysis in this patient.

Conclusion: RAI therapy is an important treatment option for patients with metastatic MSO after the initial surgical approach and total thyroidectomy. However, some MSOs may be less differentiated and not respond to RAI. Future studies are required to guide the optimal therapeutic approach for RAI refractory MSO based on the driver mutation.