This section serves as an introduction to ovarian cancer overview, highlighting the prevalence, impact, and challenges associated with this disease. Ovarian cancer is the leading cause of gynecologic cancer death in women and impacts female life and health worldwide. The high death rate in this disease is due to the late stage of disease diagnosis. Although radical surgical tumor debulking and platinum plus paclitaxel-based chemotherapy are currently established therapies for the treatment of ovarian cancer, the 5-year survival rate is still around 40%. The ability to sensitively and specifically predict the presence of early ovarian cancer, disease status, stage, and associated therapeutic efficacy has the potential to revolutionize ovarian cancer detection and treatment. Tumor markers play a critical role in the diagnosis and early detection of ovarian cancer, aiding in the identification of the disease at earlier, more treatable stages.

Consequently, identifying and validating applicable diagnostic and prognostic ovarian cancer biomarkers is essential to improving patient outcomes. Early diagnosis and detection of ovarian cancer are crucial for improving survival rates, as most cases are diagnosed at advanced stages. Ongoing ovarian cancer research is focused on the detection of ovarian cancer using novel tumor marker approaches, including the development of sensitive and specific biomarkers to enhance early detection and diagnostic accuracy.

CD9

CD9 is a member of the tetraspanin family, a group of membrane proteins involved in cell adhesion, migration, and signal transduction. Due to its expression patterns in tumor cells, CD9 has been studied for its potential as a biomarker in ovarian cancer. Research suggests that CD9 may influence tumor progression by modulating interactions between cancer cells and their microenvironment. Its presence in exosomes also makes it a candidate for noninvasive diagnostic approaches. Understanding CD9’s function could support efforts to refine detection and monitoring strategies in ovarian cancer.

Figure 1. Immunohistochemistry (Formalin/PFA-fixed paraffin-embedded sections) - Anti-CD9 antibody [EPR23105-121] (ab236630).

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Paired box 8 (PAX8)

PAX8 is a transcription factor essential in organogenesis, morphogenesis, cell growth, and differentiation. PAX8 binds a large number of genomic sites and forms transcriptional hubs. At a subset of these, PAX8, together with PRDM3, regulates a specific gene expression module involved in adhesion and extracellular matrix. PAX8 is highly expressed in benign and malignant primary epithelial ovarian carcinomas but not in metastatic ovarian cancer. PAX8 plays a critical role in ovarian carcinogenesis and ovarian tumorigenesis by participating in the molecular mechanisms underlying tumor initiation and progression.

PRDM3 is amplified in ovarian cancers. The MECOM locus and PAX8 sustain in vivo tumor growth, further supporting that the identified function of the MECOM locus underlies PAX8-driven oncogenic functions in ovarian cancer. High expression levels of PAX8 correlate with shorter survival rates, and PAX8 acts as a diagnostic and prognostic biomarker for ovarian cancer. PAX8 expression patterns can also help distinguish different ovarian cancer subtypes, aiding in accurate classification and management.

Figure 2. Immunohistochemistry (Frozen sections) - Anti-PAX8 antibody [EPR18715] (ab191870).

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MUC16

This membrane-associated mucin, also known as cancer antigen 125 (CA125), is a widely used tumor marker for ovarian cancer. It is found in the cornea and conjunctiva, in the respiratory tract, and female reproductive tract epithelium, forming a lubricating barrier against foreign particles and infectious agents. CA125 and other tumor markers are commonly used to help distinguish between benign and malignant ovarian masses and ovarian lesions, aiding in the diagnostic evaluation of ovarian cancer. However, the use of CA125 as a tumor marker has limitations, particularly in premenopausal women and postmenopausal women, as benign conditions can also cause elevated levels, leading to potential false positives. This biomarker is 79% sensitive for ovarian cancer and is considered the most reliable diagnostic marker for ovarian cancer and a potential cancer therapeutic target. Assayed as a serum biomarker for ovarian cancer diagnosis, MUC16 is also used in IHC to distinguish ovarian origins of metastases.

Figure 3. Immunohistochemistry (Formalin/PFA-fixed paraffin-embedded sections) - Anti-MUC16 antibody [EPR1020(2)] (ab110640).

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Wilms tumor protein (WT1)

This ovarian cancer biomarker is used in IHC to differentiate ovarian carcinoma (WT1+) from breast or pancreatic carcinomas (WT1-). WT1 is a key marker for identifying ovarian malignancy and for distinguishing malignant tumors from benign conditions. It is also valuable in the diagnosis of ovarian malignant tumors, especially when used in combination with other markers. According to the international ovarian tumor analysis (IOTA) consensus, standardized terminology and diagnostic criteria improve precision in classifying ovarian tumors. WT1 is a robust diagnostic and prognostic biomarker of ovarian cancers and is used in combination with PAX8 to refine diagnosis in phenotype-overlapping cases of serous cancers.

Figure 4. Immunohistochemistry (Formalin/PFA-fixed paraffin-embedded sections) - Anti-Wilms Tumor Protein antibody [CAN-R9(IHC)-56-2] (ab89901).

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p53

This tumor suppressor protein is commonly mutated in many cancer types and overexpressed in over 96% of high-grade serous ovarian cancer. p53 mutations and p53 overexpression are particularly prevalent in high-grade ovarian cancer. Both are related to shorter patient survival, with the strongest predictor of the outcome being a combination of both mutations and overexpression. As an IHC biomarker, p53 expression is used in diagnosing ovarian cancer, especially to differentiate malignant cancers (p53+) from reactive and metaplastic conditions (p53-). This utility helps improve diagnostic accuracy by distinguishing malignant from benign or reactive conditions.

Figure 5. Flow Cytometry (Intracellular) - Anti-p53 antibody [SP161] (ab227655).

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Human epididymis protein 4 (HE4)

HE4 is a protease inhibitor that is approved by the United States FDA for monitoring recurrence or progressive disease in patients with epithelial ovarian cancer. As one of the predictive biomarkers, HE4 is valuable for identifying early stage ovarian cancer and monitoring treatment response, especially when used alongside other markers. This biomarker is used in combination with MUC16 for the diagnosis of ovarian cancer, with some reports suggesting that HE4 offers increased specificity over MUC16 for the diagnosis of early ovarian cancer. HE4 also plays a significant role in improving the detection of early stage ovarian cancers, particularly when combined with other molecular markers.

Figure 6. Immunohistochemistry (Formalin/PFA-fixed paraffin-embedded sections) - Anti-HE4 antibody [EPR16658] (ab200828).

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CDKN2A/p16INK4a

cDKN2a is a tumor suppressor protein, which, when silenced in ovarian cancer, can promote carcinogenesis. Increased expression of CDKN2A, the gene product of p16INK4a, in ovarian cancer has been associated with progression and unfavorable outcomes, though this may be histotype dependent, with some studies suggesting no overall association with survival in high-grade serous tumors, block expression of this biomarker associated with shorter overall survival in endometriosis-associated carcinomas, clear cell, and endometrioid cancers, and absence of CDKN2A expression associated with shorter overall survival in low-grade serous ovarian carcinoma. Notably, CDKN2A expression is particularly relevant in endometrioid ovarian cancer, where its status may be influenced by specific genetic mutations. The use of CDKN2A as a biomarker is important in guiding ovarian cancer management decisions, especially in the context of early detection and personalized treatment strategies.

Figure 7. Western blot - Anti-CDKN2A/p16INK4a antibody [EPR1473] - C-terminal (ab108349).

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Estrogen receptor alpha

Estrogen receptor alpha is an established biomarker in the prognosis and treatment prediction of breast cancer. However, it is also emerging as a valuable biomarker in ovarian cancer. ERα staining in ovarian cancer IHC correlates with a positive response to anti-estrogen treatment (eg, tamoxifen) or chemotherapy and better clinical outcomes. Additionally, determining ERα status can help guide targeted therapy options in ovarian cancer, as it enables the selection of agents that specifically target hormone receptors and related signaling pathways in different ovarian cancer subtypes.

ERβ staining shows variable results dependent upon the stage and grade of ovarian cancer, with some studies showing negative expression, which correlates with favorable outcomes. ER expression in ovarian carcinoma is associated with better differentiated, more advanced tumors. ER levels are typically higher in high-grade, low-grade serous, and endometrioid carcinoma but lower in mucinous and clear-cell carcinoma.

Figure 8. Immunocytochemistry/ Immunofluorescence - Anti-Estrogen Receptor alpha antibody [SP1] (ab16660).

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Progesterone receptor

This biomarker is often used in conjunction with an estrogen receptor in IHC assays of ovarian carcinoma. The positivity of PR-B expression is correlated with a positive response to chemotherapy and positive patient outcomes, though it offers limited additional information over ER alone.

Figure 9. Multiplex immunohistochemistry - Anti-Progesterone Receptor antibody [SP2] (ab16661).

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Human epidermal growth factor receptor 2 (HER2)

HER2 is a tyrosine kinase that dimerizes with members of the EGFR family for activity. Under normal conditions, HER2 acts to influence cellular migration, differentiation, and interactions between cells.

HER2 mutants offer a well-established breast cancer biomarker, but their use as an ovarian cancer biomarker is more controversial. In ovarian cancer, HER2 expression is more commonly seen in the serous subtype, in older patients, and in patients with advanced-stage and high-grade differentiation cancers, leading to poor patient prognosis for ovarian cancer patients. When HER2 expression and its diagnostic or prognostic value in ovarian cancer compared to breast cancer are analyzed, HER2 is a much stronger predictive biomarker in breast cancer, while its role in ovarian cancer remains less clear and less frequently actionable.

Figure 10. Immunohistochemistry (Formalin/PFA-fixed paraffin-embedded sections) - Anti-ErbB2 / HER2 antibody [EP1045Y] (ab134182).

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Osteopontin

Osteopontin is a secreted, integrin-binding matrix phosphorylated glycoprotein that is overexpressed in many advanced cancers. It plays a role in many physiological and pathological processes, such as wound healing, inflammation, immune response, and tumorigenesis. Osteopontin is involved in ovarian tumorigenesis, contributing to the genetic and molecular mechanisms underlying the initiation and progression of ovarian cancer, and shows promise as a biomarker for early detection and prognosis. Osteopontin promotes ovarian cancer progression and cell survival and increases HIF-1alpha expression through the PI3-K/Akt pathway. Osteopontin may serve as a potential diagnostic biomarker for ovarian cancer, and could potentially influence cancer therapy and be used in the development of novel anti-tumor treatments.

Figure 11. Immunohistochemistry (Formalin/PFA-fixed paraffin-embedded sections) - Anti-Osteopontin antibody [EPR21139-316] (ab214050).

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Programmed cell death protein 1 (PD1)

This well-known immune checkpoint receptor controls lymphocyte activation by providing negative signals in conjunction with signals from lymphocyte antigen receptors. PD1 expression in ovarian cancers is associated with advanced stages of the disease in patients with high-grade tumors.

PD1 expression in IHC is an emerging biomarker for ovarian cancer diagnosis and poor patient prognosis. This biomarker is used to stratify patients for immunotherapy with PD1 inhibitors, such as nivolumab, with the therapeutic effect seen only in a subset of patients, and additional biomarkers are required to determine therapeutic efficacy accurately.

Figure 12. Multiplex immunohistochemistry - Anti-PD1 antibody [CAL20] (ab237728).

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IGFBP2

Insulin-like growth factor binding protein 2 (IGFBP2) is overexpressed in malignant ovarian tissues and ovarian cancer patients' serum and cystic fluid. IGFBP2 is frequently overexpressed in ovarian cancer tissues compared to normal ovarian tissue. IGFBP2 overexpression does not correlate with the stage of ovarian cancer. This biomarker has shown some utility in the differentiation of serous carcinoma from clear cell carcinoma for ovarian cancer diagnosis. IGFBP2 enhances the invasion capacity of ovarian cancer cells; consequently, blockage of IGFBP2 may thus constitute a viable strategy for targeted cancer therapy.

Figure 13. Immunohistochemistry (Frozen sections) - Anti-IGFBP2 antibody [EPR18012-257] (ab188200).

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Kallikrein 8

This steroid-hormone-regulated serine protease is not typically expressed in normal ovarian tissue, but elevated levels have been shown in ovarian cancers, suggesting this biomarker offers potential use in the diagnosis of ovarian cancer. Kallikreins, including Kallikrein 8, are a family of serine proteases expressed in epithelial and endocrine tissues, and their dysregulation is associated with ovarian cancer.

Kallikrein 8-positive tumors have been associated with lower-grade tumors, no residual tumor after surgery, and optimal debulking success, suggesting Kallikrein 8 may act as a favorable prognostic biomarker for ovarian cancer.

Figure 14. Western blot - Anti-Kallikrein 8/KLK8 antibody [EPR5752(2)] (ab150395).

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Cytokeratin 7 (CK7)

CK 7 is an established biomarker to differentiate primary ovarian carcinoma from metastatic colorectal carcinoma of the ovary.  This biomarker can also be used in IHC analysis of ovarian cancer to differentiate primary serous tumors (negative) from primary mucinous tumors (positive). CK7 is negatively expressed in yolk sac tumors but diffusely expressed in both clear cell carcinoma and endometrioid adenocarcinoma, making it a useful biomarker (often used in conjunction with EMA) to differentiate ovarian cancer subtypes.

Figure 15. Flow Cytometry (Intracellular) - Anti-Cytokeratin 7 antibody [EPR1619Y] - Cytoskeleton Marker (ab68459).

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Cytokeratin 20 (CK20)

CK20 is used as a biomarker in conjunction with CK7 to diagnose primary mucinous tumors of the ovary. The absence of this biomarker in CK7+ ovarian tumors is indicative of ovarian adenocarcinoma, including endometrioid, clear cell, serous, and seromucous carcinomas. CK20 is also used in pathological analysis to discriminate between ovarian tumors and secondary metastatic tumors of the ovary.

Figure 16. Immunocytochemistry/ Immunofluorescence - Anti-Cytokeratin 20 antibody [EPR1622Y] - Cytoskeleton Marker (ab76126).

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Pan-cytokeratin

This cytokeratin cocktail recognizes K1 - 8, 10, 14 - 16, and 19, but does not detect CK17 or CK18. It is commonly used in the IHC of ovarian tissue in conjunction with vimentin.

Pan-cytokeratin staining shows membranous staining in the majority of tumor types and epithelial labeling in normal tissue. Pan-cytokeratin typically shows strong staining across healthy and tumorous tissue.

Figure 17. Immunohistochemistry (Frozen sections) - Anti-pan Cytokeratin antibody [C-11] (ab7753).

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Vimentin

Vimentin is a type III intermediate filament protein that anchors the structure of the cytoplasm. In the IHC of normal ovarian tissue, vimentin localizes to surface epithelium and granulosa cells. The variable staining of this biomarker in different ovarian carcinomas, from no staining in benign mucinous tumors or serous cystadenomas to strong cytoplasmic staining in malignant serous tumors, can be used to differentially diagnose various ovarian cancer types.

Figure 18. Multiplex immunohistochemistry - Anti-Vimentin antibody [EPR3776] - Cytoskeleton Marker (ab92547).

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Forkhead box L2 (FOXL2)

FOXL2 belongs to a large family of forkhead FOX transcription factors. It is one of the first genes expressed in female gonad development, required for proper granulosa cell differentiation during folliculogenesis, and maintains a strong expression in granulosa cells throughout life. FOXL2 mutations are present in 70 - 95% of ovarian adult granulosa cell tumors but not in ovarian fibromas or ovarian juvenile granulosa cell tumors.

Consequently, IHC analysis of FOXL2 mutation is used by pathologists to distinguish diffuse adult granulosa cell tumors from cellular fibroma in ovarian tissue.

Figure 19. Immunohistochemistry (Formalin/PFA-fixed paraffin-embedded sections) - Anti-FOXL2 antibody [EPR23523-68] (ab246511).

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ARID1A

This biomarker is a member of the SWI/SNF ATP-dependent chromatin-remodeling complexes. It functions in cellular differentiation and development. Expressed in the nucleus of normal tissue, inactivation of this protein and loss of expression are seen in ~50% of ovarian clear cell carcinoma and may be an early event in the development of endometriosis-associated ovarian carcinomas. ARID1A mutations have also been implicated in hereditary ovarian cancer, suggesting a potential role in familial cancer syndromes. Additionally, emerging evidence indicates that some ovarian cancers, particularly high-grade serous carcinomas, may originate in the fallopian tube epithelium.

Figure 20. Flow Cytometry (Intracellular) - Anti-ARID1A antibody [EPR13501-73] (ab182561).

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