Malignant struma ovarii: a population-level analysis of a large series of 68 patients.

Background: Malignant struma ovarii (MSO) is a germ cell tumor of the ovary histologically identical to differentiated thyroid cancers. There is a paucity of data on this neoplasm, with fewer than 200 reported cases. The primary objective of this study was to examine the survival rate of women diagnosed with MSO using data from the Surveillance, Epidemiology, and End RESULTS (SEER) database. Secondary objectives were to describe the demographic, clinical, pathologic, and treatment characteristics of this population.

Methods: A retrospective analysis was performed of prospectively collected cancer registry data. A total of 68 patients were identified in the SEER database, 1973-2011. The chi-square test, Student's t-test, and Kaplan-Meier curves were employed for data analyses.

Results: All 68 patients were females with a mean age at diagnosis of 43.0 years. Nearly 33% underwent unilateral oophorectomy, 28.6% bilateral oophorectomy, and 28.6% oophorectomy and omentectomy, and 4.8% were treated with debulking surgery. Pelvic radiation was administered to 12.3% of patients. The mean tumor size was 52.8 mm; 80% of malignant struma ovarii were SEER staged as local. Overall survival rates at 5, 10, and 20 years were 96.7%, 94.3%, and 84.9% respectively. Among the patients, there were six deaths recorded; only one was attributed to MSO. Six individuals (8.8%) had a concomitant or subsequent diagnosis of thyroid cancer. Four patients underwent total thyroidectomy, three patients had radioactive iodine, and one patient underwent external beam radiation. Two thirds of thyroid cancers extended outside the thyroid gland. All six patients with thyroid cancer were alive at the end of follow-up.

Conclusions: It was observed that patients with malignant struma ovarii had an excellent disease-specific survival rate, regardless of the management strategy employed. However, MSO patients had a high risk for developing aggressive thyroid cancers. Therefore, MSO patients may benefit from routine thyroid imaging once the diagnosis of MSO is established.