Teratoma combined with struma ovarii and sarcomatoid carcinoma: a case report and review of the literature.

This is a rare case of struma ovarii combined with sarcomatoid carcinoma. Because struma ovarii and ovarian sarcomatoid carcinoma have an extremely low incidence, this may be the first case of a combined occurrence of both. Therefore, this report describes its clinical manifestations, diagnosis, and treatment, analyzes the pathogenesis, and summarizes the previous literature in the hope that it can be helpful to other tumor-related medical personnel and provide material support for the formation of guidelines for this disease.

Metastatic malignant struma ovarii to the pituitary presenting as a sellar mass and responding to total thyroidectomy with adjuvant radioactive iodine therapy.

Malignant struma ovarii (MSO) is a rare ovarian teratoma composed primarily of thyroid tissue. Common sites of metastasis include peritoneum, bone, liver, lung, gastrointestinal tract and omentum. We present a woman in her 50s with a history of remote oophorectomy presenting with hypopituitarism and a 2.7 cm sellar mass. Trans-sphenoidal surgery for presumed pituitary macroadenoma achieved near total resection and resultant pathology surprisingly showed ectopic thyroid tissue. The patient acquired her ovarian pathology report from Southeast Asia which showed struma ovarii of the left ovary. The pituitary mass was thus determined to be a metastatic lesion from MSO. She underwent total thyroidectomy and radioactive iodine ablation therapy with good initial response and no regrowth of the tissue or emergence of distant metastases after 5 years of annual follow-up. To our knowledge, this is the first reported case of MSO to the pituitary.

Clinical Manifestations of Malignant Struma Ovarii: A Retrospective Case Series in a Tertiary Hospital in Korea.

BACKGRUOUND: Malignant struma ovarii (MSO) is a very rare disease in which thyroid cancer originates from the ovary. Because it is rare for endocrinologists to encounter patients with MSO, endocrinologists may have a limited understanding of the disease. Therefore, we analyzed and introduced its incidence and clinical course in a tertiary hospital in Korea. METHODS: We retrospectively investigated the clinical data of 170 patients who underwent surgery for struma ovarii at the Department of Obstetrics and Gynecology of Samsung Medical Center from 1994 to May 2023. RESULTS: Among 170 patients with struma ovarii, 15 (8.8%) were diagnosed with MSO. The median age of patients with MSO was 48 years (range, 30 to 74), and the median tumor size was 3.3 cm (range, 0.5 to 11.0). Papillary thyroid carcinoma (46.7%) was the most common subtypes followed by follicular thyroid carcinoma (26.7%). All patients were diagnosed after surgery, with no predictions from preoperative imaging. The surgical extent of gynecological surgery was variable. Four patients (26.7%) underwent thyroidectomy for thyroid cancer, while one underwent total thyroidectomy and radioactive iodine therapy for MSO with peritoneal metastasis. Except for one patient who underwent hemithyroidectomy, thyroid stimulating hormone suppression therapy was performed in four patients. Only 53% of MSO patients were consulted by an endocrinologist. With a median follow-up period of 33 months (range, 4 to 156), 11 patients remained disease-free, one experienced progression with peritoneal seeding, and the remaining one was in treatment. There have been no recurrences or deaths due to MSO. CONCLUSION: An endocrinologist should be involved in establishing a therapeutic plan for MSO, for which the overall prognosis is generally favorable.

Identification of Germline FOXE1 and Somatic MAPK Pathway Gene Alterations in Patients with Malignant Struma Ovarii, Cleft Palate and Thyroid Cancer.

Germline variants in the FOXE1 transcription factor have been associated with thyroid ectopy, cleft palate (CP) and thyroid cancer (TC). Here, we aimed to clarify the role of FOXE1 in Portuguese families (F1 and F2) with members diagnosed with malignant struma ovarii (MSO), an ovarian teratoma with ectopic malignant thyroid tissue, papillary TC (PTC) and CP. Two rare germline heterozygous variants in the FOXE1 promoter were identified: F1) c.-522G>C, in the proband (MSO) and her mother (asymptomatic); F2) c.9C>T, in the proband (PTC), her sister and her mother (CP). Functional studies using rat normal thyroid (PCCL3) and human PTC (TPC-1) cells revealed that c.9C>T decreased FOXE1 promoter transcriptional activity in both cell models, while c.-522G>C led to opposing activities in the two models, when compared to the wild type. Immunohistochemistry and RT-qPCR analyses of patients' thyroid tumours revealed lower FOXE1 expression compared to adjacent normal and hyperplastic thyroid tissues. The patient with MSO also harboured a novel germline AXIN1 variant, presenting a loss of heterozygosity in its benign and malignant teratoma tissues and observable ß-catenin cytoplasmic accumulation. The sequencing of the F1 (MSO) and F2 (PTC) probands' tumours unveiled somatic BRAF and HRAS variants, respectively. Germline FOXE1 and AXIN1 variants might have a role in thyroid ectopy and cleft palate, which, together with MAPK pathway activation, may contribute to tumours' malignant transformation.

Role of gene sequencing in classifying struma ovarii: BRAF p.G469A mutation and TERT promoter alterations favour malignant struma ovarii.

AIMS: Struma ovarii (SO) are rare, accounting for 0.3-1% of ovarian tumours, and include benign and malignant lesions. In most cases, histology is not predictive of clinical outcome and prognosis. The prognosis of histologically malignant thyroid-type carcinomas can indeed be excellent, while SO, composed of normal thyroid tissue, can recur and are designated highly differentiated follicular carcinoma of the ovary. Clearer diagnostic criteria are therefore required. METHODS AND RESULTS: We retrospectively studied 31 SO using DNA and RNA sequencing with pan-cancer gene panels, including eight biologically malignant SO (BMSO) defined based on ovarian serosal or extra-ovarian dissemination at presentation or during follow-up, 10 stage IA histologically malignant SO (HMSO) with thyroid-type carcinoma morphology and 13 biologically and histologically benign SO (BSO), with none of the above-mentioned characteristics. Molecular alterations were observed in 87.5% of BMSO, 70% of HMSO and 7.7% of BSO (P < 0.001). All patients with a peritoneal dissemination at presentation or during follow-up had at least one gene alteration. BRAF mutations (44.5%) were only observed in malignant forms (HMSO and BMSO) and TERT promoter alterations (25%) only in cases of BMSO. The BRAF p.G469A mutation, which is extremely rare in thyroid carcinomas, was the molecular alteration most frequently associated with malignant SO (28.5%). CONCLUSION: Our results highlight the clinical utility of molecular sequencing in SO, based on this limited number of cases. However, as malignant SO evolve slowly, more extensive molecular studies in SO with more than 10 years' follow-up are required to draw any conclusions on the prognostic value of the associated gene alterations.

Mature cystic teratoma of the ovary with malignant transformation of tall cell subtype of papillary thyroid carcinoma.

Malignancies rarely occur in somatic parts of mature cystic teratoma of the ovary. Squamous cell carcinoma is the most common form of cancer that can develop in mature cystic teratoma. Other less frequent malignancies include melanoma, sarcoma, carcinoid, and germ cell neoplasms. Only three cases have been reported as papillary thyroid carcinoma arising in struma ovarii. We present a unique case of a 31-year-old female patient who presented with a left ovarian cyst and underwent conservative surgical management in the form of cystectomy. Histopathological examination confirmed the diagnosis of a tall cell subtype of papillary thyroid carcinoma arising from a small focus of thyroid tissue in a mature cystic teratoma of the ovary. The patient was followed up for 60 months with an uneventful clinical course. For a better understanding of such rare cancers, collaborative retrospective studies on large databases with other medical centers are required.

Struma ovarii with synchronous ascites and elevated CA125 level: a retrospective cohort study.

BACKGROUND: Benign struma ovarii (SO) with synchronous ascites and elevated CA125 level is extremely rare that the incidence, clinical characteristics, and risk factors remain unclear. METHODS: We conducted a retrospective study of patients with SO treated in our hospital between 1980 and 2022. Logistic regression was used to identify potential risk factors for SO patients presenting with ascites and elevated CA125 levels. The receiver operating characteristic (ROC) curve was used to evaluate the predictive performance of the identified risk factors. RESULTS: A total of 21 patients with synchronous ascites and elevated CA125 levels were identified in 229 patients with SO, the crude incidence rate was 9.17%, and four patients (1.75%) had pseudo-Meigs' syndrome. Ascites were completely involuted within 1 month postoperatively and the serum CA125 level decreased to normal between 3 d and 6 weeks after surgery. Multivariate logistic regression showed that age ≥49 years (OR 3.71, 95% CI 1.29 - 10.64, p = 0.015), tumor size ≥10.0 cm (OR 8.79, 95% CI 3.05 - 25.35, p < 0.001), and proliferative SO (OR 11.16, 95% CI 3.01 - 41.47, p < 0.001) were the independent risk factors for patients presenting ascites and elevated CA 125 level. The ROC curve revealed that the predictive performance for age and tumor size was unsatisfactory with an area under the curve (AUC) was 0.646 and 0.682, respectively. Linear regression demonstrated that the serum CA125 level has a moderate positive correlation with the volume of ascites (log2CA125 = 0.6272*log2ascites + 2.099, p = 0.0001, R2 = 0.5576). CONCLUSIONS: Less than one-tenth of patients with SO would present ascites and elevated CA125 levels, while age ≥49 years, tumor sizes ≥10 cm, and the presence of proliferative SO were the risk factors.

Clinical characteristics and survival outcomes in patients with primary ovarian carcinoid: A historical cohort study.

INTRODUCTION: Primary ovarian carcinoids are extremely rare ovarian tumors, and there is limited data available on their clinical characteristics and survival outcomes. MATERIAL AND METHODS: We conducted a historical cohort study of 56 patients to investigate their clinical characteristics. The overall survival, disease-specific survival, recurrence-free survival, and potential prognostic factors of these patients were also evaluated. RESULTS: The median age of these patients was 42.0 years (range: 20-71). The average mass and carcinoid size was 7.3 and 0.4 cm, respectively. Elevated tumor marker levels and ascites were observed in 15 and 10 patients, respectively. In 98.2% of the patients, tumors were confined to the ovary, while only one had metastatic disease. Surgery was the mainstay therapy: 37.5% of the patients underwent unilateral salpingo-oophorectomy, 25.0% underwent hysterectomy with bilateral salpingo-oophorectomy, 21.4% underwent ovarian cystectomy, 10.7% underwent comprehensive staging surgery, and 5.4% underwent bilateral salpingo-oophorectomy. Appendectomy and lymphadenectomy were performed in eight and five patients, respectively, but none showed tumor involvement. Chemotherapy was the only adjuvant treatment utilized, and was administered in four patients. Pathological analysis showed that strumal carcinoid was the most predominant subtype, occurring in 66.1% of the patients. The Ki-67 index was reported in 39 patients, 30 of which had an index of no more than 3%, with a maximum of only 5%. Only one relapse occurred after the initial treatment, and that patient experienced recurrences on two occasions, maintaining stable disease after surgery and octreotide therapy. After a median follow-up of 3.6 years, 96.4% of the patients achieved no evidence of disease, while 3.6% were alive with the disease. The 5-year recurrence-free survival rate was 97.9% and no death occurred. No risk factors for recurrence-free survival, overall survival, or disease-specific survival were identified. CONCLUSIONS: The Ki-67 indices were extremely low and prognoses were excellent in patients with primary ovarian carcinoids. Conservative surgery, especially unilateral salpingo-oophorectomy, is preferred. Individualized adjuvant therapy may be considered for patients with metastatic diseases.

Synchronous thyroid cancer and malignant struma ovarii: concordant mutations and microRNA profile, discordant loss of heterozygosity loci.

BACKGROUND: Struma ovarii is an unusual ovarian teratoma containing predominantly thyroid tissue. Less than 10% of cases undergo malignant transformation in the thyroid tissue and are considered malignant struma ovarii (MSO). MSO have been reported with concurrent thyroid lesions, but molecular data is lacking. CASE PRESENTATION: A 42-year-old female developed MSO and synchronous multifocal subcentimeter papillary thyroid carcinoma (PTC). The patient underwent a salpingo-oophrectomy, thyroidectomy, and low-dose radioactive iodine ablation. Both the thyroid subcentimeter PTC and MSO were positive for BRAF V600E mutation, and microRNA expression profiles were similar across all tumor deposits. However, only the malignant component demonstrated extensive loss of heterozygosity (LOH) involving multiple tumor suppressor gene (TSG) chromosomal loci. CONCLUSIONS: We present the first reported case of MSO with synchronous multifocal subcentimeter PTC in the thyroid containing concordant BRAF V600E mutations and resulting with discordant LOH findings. This data suggests that loss of expression in tumor suppressor gene(s) may be an important contributor to phenotypic expression of malignancy.

Ovarian strumal carcinoid: a case report.

BACKGROUND: Carcinoid tumors of the ovary are rare tumors, histopathologically classified as monodermal teratomas and somatic-type tumors arising from dermoid cysts. Their malignancy varies from borderline to malignant. Carcinoid tumors can occur in young and elderly women, and are sometimes seen in mature teratoma, struma ovarii, or mucinous cystadenoma as a nodule or tumor. Strumal carcinoid and mucinous carcinoid present as special types of carcinoid tumors of the ovary. CASE REPORT: This report describes a 56-year-old woman who presented with a large pelvic mass on abdominal ultrasonography during a medical examination. The diameter of the pelvic tumor was approximately 11 cm and was suspected to be ovarian cancer. The values of CA125 and CEA were above their reference intervals on preoperative examination. Abdominal total hysterectomy and bilateral salpingo-oophorectomy were performed. Intraoperative frozen-section histopathology suggested a diagnosis of mucinous adenocarcinoma; therefore, partial omentectomy and pelvic lymphadenectomy were also performed. Permanent-section histopathology led to a final diagnosis of strumal carcinoid of the ovary, stage IA (FIGO 2014). Six years post-operation, the patient had no sign of recurrence.

Computed tomography, magnetic resonance imaging, and positron emission tomography/computed tomography findings for the diagnosis of malignant struma ovarii: A case report.

Malignant struma ovarii (MSO) is an extremely rare disease arising from struma ovarii. Preoperative diagnosis is still challenging due to the lack of criteria for imaging findings. Herein, we report a case of MSO with suggestive imaging findings for a 50-year-old woman who presented with a pelvic tumor. The tumor did not typically show characteristic imaging findings of struma ovarii; however, the findings implied colloids of thyroid tissue within solid components on the magnetic resonance imaging (MRI) and computed tomography. Additionally, the solid components showed hyperintensity on diffusion-weighted image and hypointensity on apparent diffusion coefficient maps. Total abdominal hysterectomy, bilateral salpingo-oophorectomy, and omentectomy were performed. Histopathological examination revealed MSO of the right ovary, pT1aNXM0. The distribution of papillary thyroid carcinoma tissue corresponded to restricted diffusion area on MRI. In conclusion, the coexistence of imaging findings suggesting thyroid tissue and restricted diffusion in the solid component on MRI could indicate MSO.

It Does Exist! Diagnosis and Management of Thyroid Carcinomas Originating in Struma Ovarii.

Thyroid carcinoma originating in struma ovarii comprises a small minority of all cases of struma ovarii. Given the rarity of this diagnosis, literature to guide evaluation and management is limited. The most common carcinoma originating from struma ovarii is papillary thyroid carcinoma. Treatment includes surgery, including a fertility sparing approach if disease is confined to the ovary, with consideration of total thyroidectomy and radioactive iodine ablation for high-risk pathologic features or disease spread beyond the ovary. This review discusses the histopathologic findings, molecular pathology, clinical implications and management, and prognosis of thyroid carcinomas originating in struma ovarii.

Struma ovarii with massive ascites mimicking ovarian carcinoma treated with conservative laparoscopic surgery: a case report.

Struma ovarii is a rare taratoma that accounts for 0.5-1% of all ovarian tumors. It is sometimes difficult to differentiate struma ovarii from ovarian carcinoma. We encountered a case of struma ovarii that was suspected to be malignant due to the accumulation of massive ascites and an elevated CA125 level. It was successfully treated with laparoscopic surgery.A 37-year-old nulliparous woman consulted a local physician with a chief complaint of abdominal distention. Computed tomography (CT) of the abdomen revealed a pelvic tumor with a large amount of ascites. She was referred to our department. Contrast-enhanced magnetic resonance imaging (MRI) and CT showed bilateral ovarian tumors with multicystic and solid components. CA125 level was markedly elevated. Two cytological examinations of ascites showed no malignant cells. Preoperatively, malignancy was strongly suspected, but considering the possibility of a benign ovarian tumor, laparoscopic surgery was scheduled. During laparoscopic surgery, 4,850 mL of ascites were aspirated, and the left adnexa was removed. Intraoperative rapid pathology suggested struma ovarii with no evidence of malignancy. Postoperative pathology showed mature teratoma and struma ovarii.Although struma ovarii is benign in 90-95% of cases, there have been scattered case reports in which suspected malignancy led to unnecessary or excessive surgery. We propose that appropriate preoperative imaging and accurate intraoperative rapid pathology can prevent excessive surgery, conservative or laparoscopic excisions should be considered.

Current state of management of struma ovarii and preoperative imaging features: A retrospective case series study of 18 patients at a single institution.

AIM: Even though 95% of struma ovarii are benign, it is often overtreated because of the difficulty to distinguish it from malignancy. In this study, our aim was to evaluate the current state of the preoperative diagnosis and the selection of the surgical procedure, and to improve preoperative diagnostic accuracy by retrospectively reviewing imaging findings. METHODS: We retrospectively reviewed the clinical course and imaging characteristics of 18 patients who were diagnosed postoperatively with struma ovarii, pathologically, at our institution between 2015 and 2021. RESULTS: The preoperative diagnoses included benign ovarian tumor in eight cases, borderline in four cases, and malignant in six cases. None of the cases were diagnosed as struma ovarii preoperatively. Of the seven patients who had confirmed a desire for future childbearing, four patients were suspected for borderline or malignant tumor preoperatively, and underwent abdominal adnexectomy. In patients without a desire for childbearing, laparoscopic surgery was performed in only 45% of the patients whose preoperative diagnosis was benign. On magnetic resonance imaging (MRI), 54% of the cases showed enhanced solid components, which is characteristic of malignant tumors, but diffusion restriction was observed in only 11%. On computed tomography (CT), 78% of the cases showed a high attenuation lesion reflecting thyroid tissue. CONCLUSIONS: Struma ovarii is difficult to distinguish from malignancy preoperatively, making the choice of surgical approach complicated. A comprehensive evaluation of diffusion-weighted MRI and CT findings may improve the accuracy of preoperative diagnosis of struma ovarii.

Follicular carcinoma originating from struma ovarii: A case report.

INTRODUCTION: Follicular carcinoma originating from struma ovarii is a clinically rare low-grade malignant tumor. The pathological diagnosis of ovarian thyroid follicular carcinoma is predominantly based on the infiltrative growth and vascular involvement of tumor cell nests of different sizes in the ovarian parenchyma. PATIENT CONCERNS: Here we present a case of this malignancy in which the bilateral ovaries, right oviduct wall, myometrial surface, omentum, and bladder reflex were extensively involved Microscopically, the thyroid follicles in this case showed infiltrative growth of nodules of different sizes in the ovarian stroma. DIAGNOSIS: The epithelial layer of the follicles was atypical, but with no nuclear features of papillary thyroid carcinoma such as nuclear groove and nuclear pseudoinclusions. Immunohistochemistry showed positive expression of thyroglobulin, thyroid transcription factor-1, and cytokeratin19, with a Ki-67 index of 5% +. Immunohistochemical results combined with microscopic morphology allowed a diagnosis of follicular carcinoma originating from struma ovarii. INTERVENTIONS: After exclusion of contraindications to surgery, the patient underwent surgical exploration on July 26, 2022, during which frozen pathological examination was performed. OUTCOMES: The patient recovered well and was discharged. At the first follow-up visit in October 2022, the patient had an excellent survival. CONCLUSION: The analysis of the microscopic morphological characteristics and immunohistochemistry deepened our understanding of the pathological characteristics of ovarian and thyroid follicular carcinoma, and further provides a diagnostic reference for other clinicians who will encounter these conditions in the future.

Papillary thyroid carcinoma in struma ovarii: management after surgery.

A woman in her 40s presented with a 3-month history of lower abdominal pain and intermenstrual bleeding. Ultrasound of the pelvis disclosed a 4 cm left adnexal mass. An MRI of the pelvis revealed a 2.2×3.6×2.4 cm solid, enhancing left ovarian mass. Due to high suspicion for malignancy, she underwent laparoscopic left salpingo-oophorectomy and resection of the tumour. Histopathology revealed papillary thyroid carcinoma in the background of struma ovarii as confirmed by thyroglobulin and thyroid transcription factor-1 positivity on immunohistochemistry. BRAF mutation analysis was negative. An ultrasound of the thyroid gland showed two low-risk nodules. An iodine-123 whole-body scan showed normal uptake in the thyroid gland. Thyroid-stimulating hormone (TSH) was 1.070 mcIU/mL (0.450-4.500), and thyroglobulin was 6.8 ng/mL (1.5-38.5). We risk-stratified this patient as low risk for recurrence. Risk stratification of malignant struma ovarii is essential to determine suitable thyroid targeting adjuvant therapy and reduce the risk of recurrence.

Malignant struma ovarii with thyroid-type papillary and poorly differentiated carcinoma: a case report.

BACKGROUND: Malignant struma ovarii is a very rare type of gynecologic cancer. Although its most common histological subtype is a pure type of papillary thyroid carcinoma containing two components, papillary carcinoma and poorly differentiated carcinoma, malignant struma ovarii is still extremely rare. As a result, the optimal treatment for this type of tumor remains uncertain due to its rarity. CASE PRESENTATION: A 62-year-old Japanese female presented with a pelvic tumor and clinical diagnosis of malignant tumor of the ovary. She underwent complete debulking surgery, total abdominal hysterectomy, bilateral salpingo-oophorectomy, and omentectomy. The histology of the ovarian tumor revealed malignant struma ovarii with thyroid-type papillary projections and poorly differentiated carcinoma. Because of the complete resection and the absence of distant metastasis, the patient did not receive any adjuvant therapy. At 24 months after surgery, she was free of disease. CONCLUSION: This is a rare case report of malignant struma ovarii, without recurrence, in which the component was papillary thyroid carcinoma mixed with poorly differentiated carcinoma. Foregoing adjuvant therapy might be one option for malignant struma ovarii in cases with complete resection and no distant metastasis. In addition, we should consider that long-term follow-up is needed for malignant struma ovarii.

Carcinoid ovary with synchronous carcinoid tumour of the appendix: report of a rare occurrence with review of literature.

Carcinoid tumours are present in a wide range of organs but most frequently involve the gastrointestinal tract and rarely reported in gynaecological organs. Literature reports that the prevalence of ovarian carcinoid is 0.3%-1% of ovarian neoplasms and accounts for only 5% of ovarian teratomas. The pathogenesis of neuroendocrine tumours associated with synchronous primaries is undetermined and many theories have been proposed, such as existence of a common carcinogenic effect or a common stem cell undergoing similar genetic mutation. Paracrine or autocrine growth loop effect by the secretory peptides of the neuroendocrine cell tumours is also suggested. Since carcinoids are variably positive in neuroendocrine and organ-specific markers, there are no immunohistochemistry markers to delineate the definite primary site of origin versus metastasis. We report a rare case of carcinoid ovary with synchronous carcinoid tumour of the appendix. In our case, the presence of contralateral teratomatous elements may hint primary struma carcinoid instead of being metastatic from the appendix. A strumal carcinoid component was also highlighted by PAX8 positivity. This led us to conclude the case as concurrent appendix carcinoid with struma carcinoid as two independent primaries with uncertain pathogenesis. Histologically, as both tumours are well differentiated with Ki-67 of less than 3%, the decision of the joint tumour board was to keep the patient on surveillance, with no adjuvant treatment needed. The patient is currently on surveillance and the follow-up period of 24 months to date has been uneventful.

Proposed Risk Stratification and Patterns of Radioactive Iodine Therapy in Malignant Struma Ovarii.

Introduction: Malignant struma ovarii (MSO) is a rare thyroid cancer arising within an ovarian teratoma. While surgical excision of the primary tumor is widely accepted as standard of care, recommendations for adjuvant treatment of MSO-whether or not to administer radioactive iodine (RAI)-are based largely on case reports and remain debated. In this study, we aimed to propose a risk stratification and analyze RAI utilization patterns in MSO cases. Methods: The National Cancer Database (NCDB) was queried for patients with MSO between 2004 and 2016. Demographic, oncological, and clinicopathologic data were compared between groups using Fisher's exact test. Kaplan-Meier curves were used to estimate overall survival (OS), and variables associated with OS were assessed via univariate Cox regression. We adapted the 2015 American Thyroid Association risk guidelines for MSO patients. We stratified patients into low-, intermediate-, and high-risk groups using metastasis, extraovarian extension, lymphovascular invasion, lymph node status, surgical margins, tumor size, and grade. Risk stratification, demographic, oncological, and clinicopathologic data were compared between the groups receiving and not receiving RAI therapy. We then queried the Surveillance, Epidemiology, and End Results (SEER) 18 registry for patients with MSO between 2000 and 2018 to confirm our risk stratification analysis. Results: In the NCDB analysis, a total of 158 patients were identified, and 19 received RAI. RAI therapy was associated with distant metastasis (p = 0.005) and lymph node status (p = 0.012). Twenty-one NCDB patients were stratified as high risk, and 30% of high-risk patients received RAI. High-risk stratification was associated with decreased OS via univariate Cox regression (hazard ratio = 4.0 [95% confidence interval 1.11-14.26], p = 0.034). In our subsequent analysis using the SEER registry, there were 95 MSO patients, and 18 received RAI. Again, the majority of high-risk patients did not receive RAI, with only 41% of high-risk patients receiving RAI. Conclusions: MSO is a rare malignancy with apparently variable and inconsistent patterns of postoperative RAI administration. The risk stratification described here provides a framework to identify patients potentially at risk for mortality, and utilization of RAI in this group should be studied further.