Neoplasms in Struma Ovarii: A Review.

Struma ovarii is a well-known ovarian teratoma made up of benign thyroid tissue. These lesions demonstrate variable, normal architecture and normal thyroid immunohistochemical staining with positivity for TTF1, PAX8, and thyroglobulin. Though most are benign, some of these lesions can also present with a malignant component. Within this article, we review the most common diagnostic malignancies including papillary thyroid carcinoma, strumal carcinoid, highly differentiated follicular thyroid carcinoma, and other thyroid carcinomas. We additionally review the use of TTF1 staining to assist in differentiating these lesions from surrounding gynecologic epithelium, which is imperative in making such diagnoses. In highlighting these entities, we hope to provide practicing pathologists with an effective and concise review of these lesions to assist in more challenging cases of struma ovarii.

Incidence, clinical characteristics, and survival outcomes of ovarian strumal diseases: a retrospective cohort study.

BACKGROUND: Struma ovarii (SO) is a rare tumor and may transform into ovarian strumal carcinoid (OSC) and/or malignant struma ovarii (MSO), but the incidence, clinical characteristics, and survival outcomes have not been well defined. METHODS: We conducted a retrospective study of patients with ovarian strumal diseases treated in the our hospital between 1980 and 2022. Subgroup analyses of SO, OSC, and MSO were subsequently performed. RESULTS: A total of 275 cases (2.14%) were identified in a cohort of 12,864 patients with ovarian teratomas, where SO, OSC, and MSO accounted for 83.3%, 12.0%, and 4.7% of cases, respectively. There were no significant differences in age, tumor sizes, elevated tumor markers, and ascites among the three subgroups. At initial treatment, all patients with SO or OSC had FIGO stage I disease except one SO patient presenting metastatic disease, ten patients had MSO confined to the ovary, whereas other three patients had metastatic diseases. Two patients with SO respectively relapsed at peritoneum and anterior mesorectum, while none of the OSC patients presented tumor recurrence or death despite different surgical procedures employed. The 5-year recurrence-free survival rate was 88.9%, and only one death occurred at 9.5 years after diagnosis in patients with MSO. Radioiodine therapy showed satisfactory therapeutic efficacy, but these patients showed poor responses to the chemotherapy. CONCLUSION: 2.14% of ovarian teratoma could be classified as SO, of which 12.0% and 4.7% of SO may transform into OSC and MSO, repsectively. The survival outcomes were excellent even after SO transformed into OSC or MSO. SYNOPSIS: SO occupied 2.14% of ovarian teratoma, where 12.0% and 4.7% of SO may transform into OSC and MSO, respectively, and had excellent survival outcomes.

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.

Strumal Carcinoid Tumor of the Ovary: Report of Rare Occurrence with Review of Literature.

The primary ovarian carcinoid tumor is a very rare ovarian tumor, which accounts for approximately 0.5% to 1.7% of all carcinoids and 1% of ovarian cancer. According to its histopathological features, it can be divided into four categories: insular, trabecular, strumal, and mucinous, among which insular carcinoid is common in Western countries. By comparison, the chain-typed and trabecular carcinoid seem to be common in Asian countries. To date, about 150 cases have been reported in the world, and 40% of them are strumal carcinoid tumor of the ovary (SCTO), which is a highly specialized teratoma differentiated from the monomer, and often characterized by the coexistence of thyroid follicular tissue and carcinoid tissue with the neuroendocrine function. Preoperative diagnosis may be difficult due to the very insidious nature of the disease and its multiple imaging manifestations. We reported the case of a 39-year-old woman with a 5-year clinical history. Gynecologic examination and ultrasonic testing revealed an enlarged ovary with a diameter of about 60 mm, accompanied by a hypoechoic area, which was suspected to be a benign teratoma. Ca-125, AFP, free T4, TSH, and other diagnostic indicators were normal. During the laparoscopic oophorocystectomy of the left ovary, a smooth and solid tumor with the size of 6 × 6 × 5 cm was found in the right ovary. During the operation, a mature cystic teratoma containing a struma was frozen, then the oophorocystectomy of the left ovary was performed. According to the Federation International of Gynecology and Obstetrics (FIGO) in 2014, histopathological examination showed a mature teratoma with thyroid carcinoid stage Ic, and Douglas's cystic hygroma cytopathology was negative. One year after the operation, the patient was tumor-free, with Ca-125, FT4, and TSH being within the normal range. Specific diagnostic tools and serological monitoring of malignant tumors of the ovary have low specificity and sensitivity in the diagnosis of this rare malignant tumor of the ovary. Female patients with habitual constipation, chronic abdominal colic, diarrhea, and endocrine dysfunction also need to be alert to this rare malignant tumor of the ovary.

Clinical characteristics and survival outcomes in patients with ovarian strumal carcinoid.

BACKGROUND: Ovarian strumal carcinoid is an extremely rare ovarian malignant tumor with limited data on clinical characteristics and survival outcomes. METHODS: A retrospective study of 119 patients was conducted, including 98 cases identified from literature review, and their clinical characteristics were investigated. The overall survival (OS), disease-specific survival (DSS), recurrence-free survival (RFS), and potential prognostic factors of these patients were also evaluated. RESULTS: Lesions of 115 cases were confined to the ovarian while four patients presented with extra-ovarian disease upon initial diagnosis. Surgical treatment options performed in this cohort varied, 5.0% received ovarian cystectomy, 36.1% received unilateral salpingo-oophorectomy (USO), 7.6% received bilateral salpingo-oophorectomy (BSO), 42.0% received hysterectomy with BSO, and 8.4% underwent debulking surgery. Moreover, one patient did not undergo any surgery. No postoperative adjuvant therapy was administered in 89.9% patients, while 7.6% and 2.5% received adjuvant radiotherapy and chemotherapy, of which two patients received combined radiation and chemotherapy. At the final follow-up, 89.1% patients showed no evidence of the disease, and 5.0% were alive with the disease. Only seven deaths occurred, with two attributed to the tumor. The 5-year, 10-year, and 20-year OS rates were 96.0%, 85.0%, and 85.0%, respectively, with a 15-year recurrence rate of 4.4%. The 5-year and 20-year DSS rate were 98.5% and 95.9%. Multivariate Cox regression showed age ≥ 55 years was the only risk factor associated with the OS (P = 0.014, OR 7.988; 95% CI 1.519 - 42.004). However, the univariate and multivariate Cox regression showed no potential risk factor for RFS and DSS. CONCLUSION: Patients with ovarian strumal carcinoid have an excellent prognosis irrespective of the surgical option. Conservative surgery especially USO with individualized adjuvant therapy is recommended.

Ovarian Strumal Carcinoid: Case Report, Systematic Literature Review and Pooled Analysis.

Background: Ovarian strumal carcinoid is a rare tumor in which thyroid (struma) and carcinoid components coexist. The disease is generally considered to be a borderline malignancy, however, cases with metastatic disease have been described. No data in the literature are available to guide diagnosis and therapy. Methods: We performed a pooled analysis and a systematic review of histopathological-confirmed strumal carcinoid cases published in the literature using the following keywords: "strumal carcinoid of the ovary", "strumal carcinoid case report". A case of strumal carcinoid tumor diagnosed and followed-up at the Medical Oncology Unit of Spedali Civili (Brescia, Italy) was also described and included. Results: Sixty-six eligible publications were identified, providing data from one hundred and seventeen patients, plus a case diagnosed at our institution. At presentation, among the eighty-eight patients with symptomatic disease, 37% of patients suffered from abdominal distention and 49% from pain due to a growing abdominal tumor mass, 37% from constipation (peptide YY was analyzed in only nine of them, resulting above the physiologic range). Surgery was the primary therapy in 99% of the patients. Three patients had metastatic disease at diagnosis and five patients underwent recurrence after radical surgery. Histology at disease recurrence concerned the thyroid component in two patients, the carcinoid component in two patients, both histologies in one patient. Median disease-free survival and overall survival in this series were not attained. Conclusion: Strumal carcinoid of the ovary generally presents a benign behavior and surgery is curative in most cases. However, a small group of patients with this disease can undergo disease recurrence due to both the thyroid and the neuroendocrine (carcinoid) components. A follow-up in radically operated patients is therefore needed, particularly in those with a voluminous disease at diagnosis.

Clinicopathological observation of mature teratoma with malignant transformation, a single center retrospective study.

Purpose: To investigate the clinicopathological features of mature teratoma with malignant transformation. Methods: Retrospectively analysis of 1179 cases mature teratoma was done from August 1999 to December 2019 in Institution. 14 cases of mature teratoma with malignant transformation were discussed mainly for the pathological characteristics and clinical manifestations. Results: 4 of them were less than 40 years old. All but one occurred in the ovaries, and the one was in the left anterior mediastinum which was the only male. The clinical manifestations of the patients were atypical. Imaging showed cystic solid mass. Surgery was performed. Polypoid mass, solid nodule and thickened area of cyst wall can be seen on the section of tumor. Pathological results show that there were 5 cases of squamous cell carcinoma, 3 cases of carcinoid, 2 cases of serous carcinoma and 2 cases of thyroid papillary carcinoma, 1 case of carcinosarcoma and 1 case of strumal carcinoid. Two cases of squamous cell carcinoma had pelvic and abdominal metastasis. Immunohistochemistry of case 14 showed that AE1/AE3, CD56, SYN, NSE, PSAP, CDX2 were positive in carcinoid. EMA and CK20 were positive in mucinous glands around carcinoid. Calretinin and inhibin were positive in the mesenchyme adjacent to intestinal mucinous gland. Conclusions: Teratoma with malignant transformation is a rare malignancy, although teratoma is a common germ cell tumor. And it's more common in patients over 40 years, especially those patients who were in menopause. Squamous cell carcinoma is the most common type and prone to metastasis. Strumal carcinoid was well-defined, but as an endocrine tumor, it may cause a series of digestive, respiratory or hormonal disorders. Therefore, the mature teratomas should be removed in time after detection.

Strumal Carcinoid Presenting as Large Pelvic Mass: A Rare Case and Review of Literature.

Strumal carcinoid is an unusual rare ovarian teratoma characterized by the presence of thyroid tissue with a carcinoid tumor. We report a case of a 60-year-old nulliparous woman, who presented with complaints of a decrease in appetite, urinary frequency, and left lower extremity edema. By ultrasound of the abdomen, a large multiloculated cystic lesion occupying almost the entire pelvis and measuring 24 x 14 x 20 cm with internal debris concerning either uterine or ovarian cystic carcinoma was seen. By MRI, it was confirmed to be an ovarian lesion. Labs revealed elevated cancer antigen 125 (CA125) of 105 U/ml and carcinoembryonic antigen (CEA) of 6.4 ng/ml. The patient underwent surgery and the intraoperative consultation confirmed teratoma with a neuroendocrine component. Grossly, it was a multicystic ovarian mass and on sectioning, it had partial solid and cystic areas with clear to mucoid fluid. Histopathology showed foci of ectopic thyroid tissue admixed with foci of well-differentiated neuroendocrine tumor, grade 1 (carcinoid) displaying insular and trabecular patterns consistent with the diagnosis of strumal carcinoid (monodermal teratoma). Thyroid transcription factor-1 (TTF-1) and thyroglobulin immunostains highlighted ectopic thyroid tissue and synaptophysin highlighted neuroendocrine component. Strumal carcinoids are almost invariably benign and pathologic staging is not warranted. Treatment of strumal carcinoid is salpingo-oophorectomy.

Multiple malignant transformations of an ovarian mature cystic teratoma.

BACKGROUND: Malignant transformation of mature cystic teratomas (MCTs) is a rare phenomenon. The most common histology of a malignant transformation is squamous cell carcinoma, and there are limited reports of multiple malignancies arising in a single MCT. Further data are necessary to guide management of these atypical cases. CASE: We present the case of a 48-year-old with MCT containing a malignant papillary thyroid carcinoma (PTC) arising in the context of struma ovarii and a carcinoid tumour. CONCLUSION: Malignant transformations of MCTs are exceedingly rare with no guidelines on management. We use this case to demonstrate an approach for the workup and management of malignantly transformed MCTs.

Immunohistochemical Profile and 47-Gene Next-Generation Sequencing (NGS) Solid Tumor Panel Analysis of a Series of 13 Strumal Carcinoids.

Strumal carcinoid is an extraordinary rare tumor of the ovary consisting of thyroid tissue intermixed with neuroendocrine tumor component. The cellular origin of strumal carcinoids has been an area of debate. There is also little data on detailed immunohistochemical and molecular characteristics of these neoplasms. For this reason, this series investigated the characteristics of a series of 13 strumal carcinoids using immunohistochemical markers and a 47-gene next-generation sequencing (NGS) solid tumor panel analysis. Both cellular components showed thyroglobulin expression in all tumors. TTF-1 expression was noted in both cellular components of 11 cases. Chromogranin A was positive in both components of most tumors (n = 12, 92.3% in the neuroendocrine component and n = 10, 76.9% in the thyroid follicular component). Synaptophysin stained the neuroendocrine component of all cases, and it was also identified in the follicular thyroid component of a single case. All tumors were negative for CDX2 and calcitonin. ISLET1 was positive in the neuroendocrine component of 8 cases (6.5%). With the exception of one case, all tumors were positive for SSTR2a. The tumors were associated with a low Ki67 labeling index. All cases were microsatellite stable and no pathogenic mutations were identified using a 47-gene NGS solid tumor analysis. This series underscored that strumal carcinoids are distinct neuroendocrine tumors. The synchronous expression for thyroid follicular epithelial and neuroendocrine differentiation biomarkers may suggest a precursor cell origin displaying mixed-amphicrine differentiation. While strumal carcinoids can be diagnosed by their typical morphology and immunohistochemical profile, frequent SSTR expression may serve as a potential theranostic biomarker in the management of affected patients. In addition, the absence of common driver mutations in the NGS solid tumor panel may suggest that these neoplasms seem to be genetically unrelated to follicular epithelial-derived thyroid tumors and potentially different than other commonly identified well-differentiated neuroendocrine neoplasms. Therefore, further studies focusing on molecular characteristics of this entity are still needed.

Metastatic Bilateral Strumal Carcinoid: A Case Report and Review of the Literature.

Primary ovarian carcinoids are very rare tumors that belong to the germ cell family of ovarian malignancies. They account for less than 1% of all carcinoid tumors and for less than 0.1% of all ovarian neoplasms. Recurrences are even rarer, with only few cases reported in the literature. Strumal carcinoid has recently been recognized as an extremely rare distinct entity. We report on a patient with bilateral mature cystic teratoma with millimetric foci of ovarian strumal carcinoid who developed lymph node para aortic metastasis after 30 years from primary diagnosis. Our case is thus far the second report of a metastatic strumal carcinoid and the first one in which strumal carcinoid occurred bilaterally and was also metastatic.

Imprint cytology of strumal carcinoid of the ovary: A case report with immunocytochemical analysis.

Strumal carcinoid is a rare ovarian tumor defined as carcinoid associated with struma ovarii. We report here the second cytological case of strumal carcinoid and performed immunocytochemical analysis for the first time. A 68-year-old Japanese female was found to have a solid tumor with small cystic components in the left ovary, and bilateral salpingo-oophorectomy was performed. The Papanicolaou smear of the imprint cytological specimen of the left ovarian tumor revealed presence of two distinct components. The first component included thyroid follicles, which was composed of flat sheets of polygonal epithelial cells without nuclear groove and intranuclear inclusion. The other component was composed of trabecular clusters of columnar cells containing round to slender nuclei with "salt and pepper" chromatin. Immunocytochemical analysis revealed that synaptophysin was expressed in the latter component. Therefore, a cytodiagnosis of strumal carcinoid was made. Histopathological analyses confirmed the diagnosis of strumal carcinoid. Albeit rare, carcinoid tumor occurs in the ovary, and the recognition of characteristic nuclear features and cellular arrangement leads to correct cytodiagnosis. Presence of struma ovarii component suggests an ovarian origin. Moreover, immunocytochemical analysis for neuroendocrine markers aids its differential diagnosis from granulosa cell tumor and carcinoma arising from struma ovarii.

Ovarian Strumal Carcinoid Tumour: Case Report.

BACKGROUND: Ovarian strumal carcinoid is a germ cell tumour characterised by a mixture of thyroid tissue and carcinoid. Ovarian struma is a very rare occurrence with 0.3-1% incidence of all ovarian tumours and 3% of mature teratomas. Primary carcinoid ovarian tumours are still uncommon as a part of mature teratoma or mucinous cystadenoma. There are four major variants of a carcinoid tumour: insular, trabecular, strumal and mucinous. A strumal carcinoid is an unusual form of ovarian teratoma composed of an intimate admixture of thyroid/carcinoid tissues. CASE REPORT: This is a case report of a 59-year old woman with a 5-year clinical history of perimenopausal uterine bleeding and three explorative curettages. Gynaecological and ultrasound examinations revealed ovarian enlargement with a diameter of 50 mm with hypoechoic zones suspected of benign teratoma. The diagnostic test such as Ca-125, AFP, free-T4 and TSH was in normal range. A smooth, solid right ovarian 50 an mm-size tumour, as well as small amount of fluid in the Douglas pouch, was found during the total abdominal hysterectomy, bilateral salpingo-oophorectomy and staging biopsy. The histopathology revealed teratoma with strumal carcinoid tumour IA stage according to AJCC 2010 of the right ovary and negative cytopathology of the fluid from the Douglas pouch. On the postoperative 2-year control, the patient was tumour free, and Ca-125, free-T4 and TSH were in normal range. CONCLUSION: We would like to point out those specific diagnostic tools, such as ultrasound and Ca-125 have low specificity and sensitivity in detection of this rare ovarian malignancy.

Strumal carcinoid of the ovary - report of two cases and review of literature.

OBJECTIVE: Strumal carcinoid (SC) is a rare ovarian germ-cell tumour, which is characterized by a mixture of thyroid tissue and carcinoid. It can be presented as a monodermal teratoma or as a part of mature cystic teratoma (dermoid cyst). DESIGN: Case report. SETTING: Department of pathology, St. Elisabeth Cancer Institute, Bratislava. METHODS AND RESULTS: Hereby the authors describe two cases of this rare tumour in clinically asymptomatic women, 46- and 52-year-old, whom tumours were diagnosed at preventive gynaecological examination. The tumours considered of solid - cystic features, measured 65×45×40 mm and 75×45×40 mm and both contained parts of SC represented by tougher yellowish gelatinous areas. In both cases, SC was a part of the mature cystic teratoma (dermoid cyst), with predominated content. Histologically, both SC had a characteristic composition of intimate mixture of mature thyroid tissue and carcinoid. Immunohistochemically, the thyroid tissue stained positively with cytokeratin7, thyroglobulin and thyroid transcription factor-1, and the carcinoid component exhibited expression of synaptophysin and chromogranin A (only in one case). Tumour cells of both components of SC were negative for calcitonin and carcinoembryonic antigen. Both tumours showed low proliferation activity expressed by Ki-67 (up to 2%). Tumours were diagnosed in stage IA, and up to now are patients without any complications associated with tumours, free of relapse for 3 years and 6 months, respectively. CONCLUSION: SC represents an interesting form of primary ovarian carcinoid, which is usually asymptomatic and when confined to ovary, mostly has benign behaviour and can be treated by simple one-sided or bilateral adnexectomy. Keywords ovary, germ cell tumours, strumal carcinoid, immunohistochemistry.

Peptide YY producing strumal carcinoid tumor of the ovary in a postmenopausal woman: a rare cause of chronic constipation.

Strumal carcinoid tumor of the ovary is a rare subtype of ovarian carcinoid tumors; it is characterized by an intimate mixture of thyroid and carcinoid tissues. We present a case of a 64-year-old woman who presented with the chief complaint of persistent, severe constipation for over 5 years; she was later found to have an ovarian strumal carcinoid tumor. Computed tomography showed a well-defined solid mass measuring 6.4 cm at the right adnexa. The patient underwent right salpingo-oophorectomy and was histopathologically diagnosed as having a strumal carcinoid tumor. Immunohistochemical examination showed immunoreactivity for peptide YY (PYY), which exerts an inhibitory effect on the peristaltic actions of the distal intestine. After surgery, the patient's constipation resolved rapidly, suggesting a correlation between PYY producing ovarian carcinoid tumor and constipation. This is the first case report of PYY producing primary strumal carcinoid tumor of the ovary associated with persistent, severe constipation from Korea.

Peptide YY producing strumal carcinoid tumor of the ovary in a postmenopausal woman: a rare cause of chronic constipation

Strumal carcinoid tumor of the ovary is a rare subtype of ovarian carcinoid tumors; it is characterized by an intimate mixture of thyroid and carcinoid tissues. We present a case of a 64-year-old woman who presented with the chief complaint of persistent, severe constipation for over 5 years; she was later found to have an ovarian strumal carcinoid tumor. Computed tomography showed a well-defined solid mass measuring 6.4 cm at the right adnexa. The patient underwent right salpingo-oophorectomy and was histopathologically diagnosed as having a strumal carcinoid tumor. Immunohistochemical examination showed immunoreactivity for peptide YY (PYY), which exerts an inhibitory effect on the peristaltic actions of the distal intestine. After surgery, the patient's constipation resolved rapidly, suggesting a correlation between PYY producing ovarian carcinoid tumor and constipation. This is the first case report of PYY producing primary strumal carcinoid tumor of the ovary associated with persistent, severe constipation from Korea.

Pathology of Struma Ovarii: A Report of 96 Cases.

Thyroid tissue is a relatively frequent component of mature teratoma and can occur in 5-20 % of cases. Struma ovarii is defined as ovarian goiter which comprises either entirely or predominantly thyroid tissue (>50 %). This also includes cases of mature teratoma with less than 50 % thyroid tissue but harboring thyroid-associated malignancy. A total of 118 patients with mature teratoma containing thyroid tissue were identified at our institution (1989 to 2014). Ninety-six cases were diagnosed struma ovarii, including 10 cases of papillary thyroid carcinoma, 1 case of highly differentiated follicular carcinoma of ovarian origin (HDFCO), 5 cases of strumal carcinoid, and 80 cases of struma ovarii (53 cases of thyroid-only struma ovarii). Six cases had diffuse adenomatous hyperplasia, and seven cases had focal adenomatous hyperplasia. There was no recurrence on follow-up except one of the papillary thyroid carcinomas. Concurrent primary ovarian lesions included: serous cystadenoma--3, mucinous cystadenoma--4, Brenner tumor--3, thecoma--2, ovarian fibroma--1, and focal hilus cell hyperplasia--4 cases. In this series, papillary thyroid carcinoma and strumal carcinoid were the most common well-differentiated neoplasm/malignancies arising in struma ovarii; these demonstrate a minimal or no aggressive clinical behavior.

Papillary thyroid carcinoma in ovarian strumal carcinoid tumor: case report / Carcinoma papilífero de tireoide em tumor carcinoide strumal de ovário: relato de caso

Strumal carcinoid tumor is an uncommon type of ovarian teratoma containing thyroid and carcinoid tissue. We report the case of a 49 year-old patient with menstrual irregularity. The ultrasonographic imaging revealed a mass in the left ovary. The histopathological assessment showed a papillary thyroid carcinoma in a strumal carcinoid tumor.

Carcinoide strumal é uma forma incomum de teratoma ovariano que contém tecido tireoidiano e carcinoide. Relatamos o caso de uma paciente de 49 anos de idade, cuja investigação por irregularidade menstrual revelou massa em ovário esquerdo à ultrassonografia. A avaliação histopatológica da massa apresentou carcinoma papilífero de tecido tireoideano em carcinoide strumal.

Cytopathologic characteristics of the primary strumal carcinoid tumor of the ovary: a case report with emphasis on differential diagnostic considerations.

Primary strumal carcinoid tumor of the ovary (SCTO) is an extremely rare entity, though the survival rate is excellent if the disease is confined to one ovary. A case is presented here in which intraoperative squash smears in a 45-year-old woman with a left adnexal mass revealed dispersed or small clusters of neoplastic cells forming loosely cohesive gland-like structures with abundant cytoplasm. The nuclear chromatin was finely granular with a "salt and pepper" appearance and occasional tiny nucleoli. The position of the nucleus presented a vaguely plasmacytoid appearance. Small fragments of thyroidal colloid-like structures were also identified. A cytopathologic diagnosis of a SCTO was suggested. Further evaluation and immunohistochemical studies were conducted on formalin-fixed, paraffin-embedded material. Cords or nests of uniform cells with abundant cytoplasm, and eccentric nuclei with coarse chromatin and occasional colloidal tissue were identified on H&E sections. The tumor cells showed diffuse and strong cytoplasmic staining for chromogranin A, synaptophysin, CD56, and vimentin but were negative for calretinin, α-inhibin or CDX2. The proliferative index with MIB-1 was around 3%. Thyroidal colloid-like structures were immunoreactive for thyroglobulin and TTF-1 stains. The diagnosis of primary SCTO was confirmed based on cytopathologic, histopathological, and immunohistochemical results, and the location of the tumor. Awareness of the cytopathological findings of SCTO can assist in diagnosing this rare entity correctly.