Ovarian sex cord-stromal tumor (SCST) is a group of tumors composed of a single or a mixture of differentially differentiated “sex cord-like” cells, gonadal mesenchymal components, and various flavinized cells. “The complexity of ovarian embryonic development determines the multi-directional differentiation of ovarian gonadal-mesenchymal tumors, and therefore the classification is also complex. In clinical practice, some pathological types are not familiar to clinical or pathologists, which affects the correct diagnosis and treatment of patients. Immunohistochemical techniques have become an indispensable adjunct to our routine pathological diagnostic work. The application of this technique in ovarian SCST can be more precisely summarized as “new role for old markers”, because although there are few new specific markers for SCST in recent years, some markers commonly used in other tumors, such as calretinin, melan-A, etc., have been found to play an important role in the diagnosis and differential diagnosis of SCST one after another. In this paper, we combine our clinical experience and our experience with other tumor markers. In this paper, we analyze various markers used in SCST and review the application of immunohistochemical techniques in the diagnosis of ovarian SCST and their limitations, in order to raise awareness and use immunohistochemical techniques more rationally for the accurate diagnosis of ovarian SCST. I. Application of α-inhibin in the diagnosis and differential diagnosis of SCST Inhibin (inhibin) is the most specific marker for the diagnosis of ovarian SCST, which is a heterodimeric glycoprotein-like hormone composed of α and β subunits and belongs to the transforming growth factor-β superfamily. support-lesion cell tumors, amphiblastomas and steroid cell tumors, but is only weakly expressed or not expressed in spindle cell tumors such as ovarian fibroids and fibrous follicular membranous tumors. SCST with predominantly sex cord-like components (e.g., granulosa cell tumors, supportive cell tumors, etc.) often need to be differentiated from ovarian endometrioid adenocarcinoma because the latter may also have hollow tubular, long cord-like or trabecular arrangement of the epithelium, and the nuclei may contain nuclear grooves and luteinized mesenchymal cells; granulosa cell tumors with cystic or degenerative changes may form pseudopapillae, which also need to be differentiated from migratory cell carcinoma or plasma breast carcinoma It also needs to be distinguished from metastatic cell carcinoma or plasma breast carcinoma. If typical epithelial carcinoma components are not found, immunohistochemistry can be used as an aid. Ovarian epithelial carcinoma does not express α-inhibin or calretinin, but expresses EMA and CK7, while the majority of ovarian SCST expresses broad-spectrum Keratin, but generally does not express EMA or CK7, with only isolated reports of juvenile granulosa cell tumors that are weakly positive for focal CK7. Therefore, the combination of α-inhibin, calretinin and EMA, and CK7 staining can basically distinguish SCST from epithelial carcinoma. Ovarian granulosa cell tumors (especially juvenile granulosa cell tumors) should also be differentiated from hypercalcemic small cell carcinomas, which have common features including the predilection for young women, the appearance of follicular structures in histomorphology, and active nuclear schizophrenic images. However, the immunophenotype is different, with hypercalcemic small cell carcinoma being negative for α-inhibin and CD99 and positive for EMA. Support cell tumors need to be differentiated from ovarian carcinoid tumors and Wolffian adnexal tumorWAT, because carcinoid tumors can have a striated structure and WAT can have a tubular growth pattern, and both striated and tubular structures are seen in support cell tumors. However, because the expression rate of both inhibin and calretinin in WAT can reach over 70%, but the coloration is weak and limited compared with that of supporting cell tumors, inhibin or calretinin is not very helpful in distinguishing supporting cell tumors from WAT, and can only be relied on for identification. WAT is usually located in the broad ligament, the plasma surface of the fallopian tube, and the ovarian hilum, and its main histologic features include solid areas composed of spindle cells, tubules composed of columnar cells, reticular structures, and multicystic lacunae composed of cuboidal and dwarf cuboidal cells. II. calretinin in the diagnosis and differential diagnosis of SCST Calretinin is a calcium-binding protein with a molecular weight of 29 kDa. It was initially thought to be a specific marker for mesothelioma, but recently it has been found to be expressed in inner theca cells, hilar cells, and luteinized mesenchymal cells of the ovary. As mentioned before, calretinin is often combined with inhibin. Most studies have confirmed that calretinin is more sensitive than inhibin and is expressed in both sex cord-like and mesenchymal components, especially in ovarian fibrous tumors and follicular membranous tumors where calretinin expression is superior to inhibin, and in ovarian steroid cell tumors where calretinin is strongly and diffusely positive with cytoplasmic and nuclear staining. In other types of SCST, calretinin tends to be strongly positive in a patchy and localized manner, whereas inhibin expression is often more focal and weak. However, the specificity of calretinin is low and more than 1/5 of ovarian epithelial tumor tissues are positive. In addition, calretinin is also expressed in WAT, smooth muscle tumors, carcinoid tumors, hypercalcemic small cell carcinomas, metastatic lobular carcinomas of the breast, and fibroproliferative small round cell tumors. Therefore calretinin must be used in combination with inhibin for the differential diagnosis of ovarian SCST. Because calretinin is positively expressed in both normal endometrial mesenchymal and endometrioid mesenchymal sarcoma, calretinin is of little value in differentiating SCST from endometrioid mesenchymal sarcoma. Melan-A in the diagnosis and differential diagnosis of SCST Melan-A is present in normal melanocytes and most of their associated benign and malignant tumors. Melan-A is expressed in about 80% of melanomas and tumors with melanocyte differentiation (e.g., perivascular cell tumors, soft tissue clear cell sarcomas, etc.). Melan-A is also a sensitive marker for steroid hormone-producing cells such as the adrenal cortex, and is expressed in ovarian hilar cells, granulosa cells, endovascular cells, and mesenchymal cells. Studies have shown that Melan-A is highly expressed in ovarian steroid cell tumors and can also be focally positive in other SCSTs, including supportive-lesional cell tumors, granulosa cell tumors, sclerosing mesenchymal tumors, and fibrous-follicular membrane tumors. In particular, the Ledi cell component is more strongly expressed in supportive-Ledi cell tumors, and Melan-A expression is associated with differentiation of supportive-Ledi cell tumors. This marker was negative in ovarian epithelial carcinoma and endometrioid mesenchymal tumors, but uterine tumors with sex cord-like differentiation and WAT can have positive melan-A expression. The sensitivity and specificity of Melan-A in the diagnosis and differential diagnosis of SCST are between that of inhibin and calretinin, especially in steroid cell tumors and tumors with male sex cord differentiation, which should be noted when choosing the combination of differential diagnostic markers. Application of WT1 in the diagnosis and differential diagnosis of SCST WT1 is a Wilms tumor suppressor gene, located on chromosome 11p13, which plays a role in tumorigenesis and normal development of urogenital. WT1 has been found to be expressed in granulosa cells, and its role may be to attenuate alpha-repressor promoter activity, thereby blocking follicular development. Although WT1 plays a regulatory role on Inhibin, the two have not been shown to be correlated in expression. According to the literature, most gonadal-mesenchymal tumors are diffusely positive for WT1, except for steroid cell tumors, and in particular, SCST with gonadal-like component differentiation, i.e., supportive cell tumors and granulosa cell tumors, have strong WT1 expression and those with gonadal mesenchymal differentiation have weak expression. Among non-gonadal mesenchymal tumors of the ovary, ovarian epithelial carcinomas also frequently express WT1, especially plasmacytoma and migratory cell carcinoma, while the expression rate is lower in endometrioid carcinoma and clear cell carcinoma; WT1 is also positive in hypercalcemic small cell carcinoma, mesothelioma and pro-fibroproliferative small round cell tumors; but not in ovarian carcinoid tumors. Therefore, WT1 can be regarded as an effective complementary marker to inhibin, but its application is limited in view of its low specificity. V. CD99 in the diagnosis and differential diagnosis of SCST CD99 (MIC2) is a 32-kDa transmembrane glycoprotein formed by the glycosylation of a 28-kDa precursor molecule with O. CD99 is expressed in normal supporting cells, granulosa cells and mesenchymal cells. CD99 was expressed in SCST and correlated with differentiation, such as higher expression in juvenile granulosa cell tumors and highly differentiated supporting-lymphocytes; it was absent or weakly expressed in ovarian fibrous tumors, follicular meningiomas and lymphoblastic tumors, and only weakly positive in steroid cell tumors. CD99 was once thought to be a more specific marker for granulosa cell tumors, but it was later found that CD99 is also expressed in ovarian plasmacytoma, mucinous, endometrioid carcinoma and clear cell carcinoma, as well as yolk cystic tumor and pro-fibroblastic small round cell tumor. Therefore, the sensitivity and specificity of CD99 in the diagnosis of SCST are poor, and it has a tendency to be gradually replaced by other markers in the differential diagnosis of SCST. CD56 is a cell surface glycoprotein related to neural cell adhesion molecules, which plays an important role in embryogenesis and interconnection of neural cells. expression. Recently, CD56 was also found to be a more sensitive indicator of ovarian SCST, and although it is not expressed in normal granulosa cells and follicular cysts, it is moderately-strongly positive in granulosa cell tumors, supportive-lymphocytomas, sclerosing mesenchymal tumors, steroid cell tumors, and cyclic tubular structural sarcomas, and in Fibromas were also positive to varying degrees. CD56 seems to be more sensitive than inhibin and calretinin, but its specificity is very poor and it is expressed in endometrioid and carcinoid tumors, so its value in the differential diagnosis of routine SCST is very limited. VII. CD10 in the diagnosis and differential diagnosis of SCST CD10 was originally described as a tumor-specific antigen for lymphoblastic leukemia, and it is a metalloendopeptidase with a molecular weight of 90-120 daltons. In female genital tissues, CD10 was initially considered as a specific marker for the endometrial mesenchyme and its tumors. Later, it was found that ovarian mesenchymal cells and SCST could also express CD10. studies confirmed that CD10 was expressed in all SCST except ovarian fibroma, especially follicular meningioma, sclerosing mesenchymal tumor and steroid cell tumor. However, the intensity of CD10 expression (staining) tended to be weak in all tumors, which is different from the diffuse strong positivity of endometrial mesenchymal tumors. Although simple endometrioid mesenchymal components do not express inhibin, areas of sex cord-like differentiation can show positive for inhibin. Therefore, if used to differentiate SCST from endometrial mesenchymal sarcoma, the combination of CD10 and Inhibin must be used, especially when comparing the intensity and range of staining of different antibodies. In addition, WAT and hypercalcemic small cell carcinoma also express CD10, so CD10 cannot be used to distinguish SCST from WAT and hypercalcemic small cell carcinoma. SF-1 and other markers in the diagnosis and differential diagnosis of SCST Steroidogenic factor 1 (SF-1), also known as adrenal 4-binding protein (Ad4BP), is a nuclear transcription factor that regulates genes related to steroidogenesis, adrenal and gonadal development. Ad4BP is a nuclear transcription factor that regulates genes related to steroidogenesis, adrenal and gonadal development, etc. Recently, it has been reported that SF-1 is expressed in 100% of ovarian supportive cell tumors, but not in endometrioid and carcinoid tumors, so it may play a role in differential diagnosis, and may be a better differential marker after inhibin. Because of the limited reports in the literature, further confirmation is needed. Other markers such as vimentin, Mullarian inhibiting substance and S100 protein are also expressed in SCST to varying degrees, but their specificity or/and sensitivity are poor, and their application in diagnosis and differential diagnosis is limited, so we will not repeat them here. It is worth mentioning that we met a patient with ovarian supporting mesenchymal stromal cell tumor whose serum AFP was elevated and immunohistochemical staining also showed positive AFP in the supporting cell component. Similar rare cases have been reported in the literature, and care should be taken to avoid being misled by immunohistochemical results during diagnosis. Although the classification of ovarian SCST is complex, careful observation of the gross specimen and routine stained sections under light microscopy can lead to an accurate diagnosis in most cases. Given that the majority of tumors in this group are functional in nature, the importance of clinicopathologic linkage should be particularly emphasized. When performing pathological examination and diagnostic/differential diagnosis, care should be taken to carefully search for typical pathological changes among the atypical ones, and if immunohistochemistry is required to aid in the diagnosis, multiple combinations of relevant markers should be selected. Most importantly, the expression profile of the above-mentioned markers in ovarian SCST and suspected tumors should be clear in mind, and the interpretation of immunohistochemical staining results must be based on morphological features and comprehensive analysis.