Endocrine Abstracts

Introduction: Malignant struma ovarii is a rare disease, for which risk factors and prognostic features are not well-defined. We present a patient with concomitant Graves’ disease and metastatic follicular thyroid cancer arising from struma ovarii, and discuss the possible mechanism of this association.

Clinical case: A 43 year old woman undergoing follow-up for Graves’ disease (GD) presented with an enlarging left lower abdominal mass. She had a prior history of a left ovarian cystic teratoma with struma ovarii (SO), which had been resected at age 34 years. There was no record of thyrotoxicosis at the time. GD was diagnosed at age 43, when she presented with weight loss, palpitations, and tremours. Free T4 was 48.5 pmol/l [11.8–24.6], TSH < 0.005 mIU/l [0.27–4.2], and TRAb 2.7 IU/l [<1.8] at diagnosis. Thyroid ultrasound (US) revealed heterogenous parenchymal echotexture and increased vascularity. She was started on carbimazole. 4 months later, she reported a sensation of lower abdominal fullness. Pelvic US showed a heterogenous left adnexal mass, measuring 13.8 × 11.6 × 7.1 cm. Left salpingo-oopherectomy followed. Intra-operatively, peritoneal nodules were visualised; histology confirmed intra-ovarian thyroid tissue housing a highly-differentiated follicular thyroid carcinoma, with metastatic peritoneal deposits. Computed tomography of the chest and abdomen did not show any gross evidence of distant metastasis. Completion hysterectomy, right salpingo-oopherectomy, omentectomy, and debulking surgery was performed. Intra-operatively, more metastatic foci were identified on the right fallopian tube and infundibulopelvic ligament, uterovaginal fold, bladder and rectal walls, and peritoneum. A total thyroidectomy followed; histology showed no evidence of intra-thyroidal malignancy. I-131 therapy was administered. The post-therapeutic I-131 whole body scan revealed multiple intra-abdominal foci of uptake, representing remnant disease. At 1 year’s follow-up, the patient remains on levothyroxine therapy, with a TSH goal of <0.1 mIU/l. A repeat radioiodine scan is planned. Anti-TG titres have trended downward, and she remains clinically well.

Discussion: To our knowledge, this is the first reported case of metastatic malignant SO in the setting of GD. GD appears to be associated with an increased incidence of differentiated thyroid cancer (DTC); DTC in these situations might behave more aggressively. This association may well apply to the risk of malignant transformation in SO tissue. TSH receptor antibody and local cytokine production might contribute to the pathophysiology.