Tumor Marker Overview
Tumor markers are soluble glycoproteins that are found in the blood, urine, or tissues of patients with certain types of cancer. They are typically produced by tumor cells, but in some cases they may be produced by the body in response to malignancy or to certain benign conditions. Tumor markers are not elevated in all cancer patients, particularly patients with early-stage cancer. The various tumor markers differ in their usefulness for screening, diagnosis, prognosis, assessing therapeutic response, and detecting recurrence. 
Normalization of tumor marker values may indicate cure despite radiographic evidence of persistent disease. In this situation, residual tumor is frequently nonviable. Sometimes, tumor marker values may rise after effective treatment (due to cell lysis), but the increase may not portend treatment failure. A consistent increase in a tumor marker value, combined with lack of clinical improvement, may indicate treatment failure. Residual elevation after definitive treatment usually indicates persistent disease.
Many new tumor markers have been discovered since the development of monoclonal antibodies, and most tumor markers are now detected with them. No marker is completely specific. Therefore, diagnostic immunohistochemistry must be used in conjunction with morphologic and clinical findings. 
Types of gynecologic tumor markers
Ovarian cancer, uterine cervical cancer, endometrial cancer, and trophoblastic neoplasms are gynecologic malignancies for which tumor markers are in clinical use. The following are important gynecologic tumor markers:
Cancer antigen 125 (CA-125)
Beta human chorionic gonadotropin (beta-hCG)
Urinary gonadotropin fragment
Carcinoembryonic antigen (CEA)
Squamous cell carcinoma (SCC) antigen
Müllerian inhibiting substance (MIS)
Carbohydrate antigen 19-9
Cancer antigen 27-29
Human telomerase reverse transcriptase (hTERT)
Other potential gynecologic tumor markers include the following:
MIB1-determined tumor growth fraction
Human epididymis protein 4 (HE4)
Vascular endothelial growth factor (VEGF)
Interleukin 8 (IL-8)
Macrophage colony-stimulating factor (M-CSF)
Insulinlike growth factor–binding protein-3
Tumor-associated trypsin inhibitor
Clinical usefulness of tumor markers
The usefulness of a tumor marker is in its sensitivity and specificity, as well as its influence on patient management decisions. Because pathologic diagnosis of ovarian cancer is difficult without laparotomy, tumor markers such as CA-125, in addition to diagnostic imaging, are useful in preoperative evaluation for ovarian cancer.
No tumor markers with high sensitivity and high specificity for endometrial cancer are known at present, although CA-125 is often used in clinical practice. However, in a retrospective analysis (2008-2011) evaluating the utility of preoperative tumor markers in predicting prognostic parameters in women with pure endometrioid type endometrial cancer who underwent adjuvant therapy, investigators noted elevated levels of CA-125 was significantly able to predict for the following  :
Tumors larger than 2 cm
Invasion of the lymphovascular space and of the deep myometrium
Involvement of the cervix and adnexa
Lymph node metastasis
Requirement for adjuvant treatment
In addition, mean levels of CA-15-3 and CA-19-9 were significantly higher in women who required adjuvant therapy, and levels of CA-19-9 were also predictive of deep myometrial invasion, cervical involvement.  CEA and AFP levels were inadequately able to predict any of the evaluated poor prognostic parameters and requirements for adjuvant treatment. 
SCC antigen is useful in the clinical management of advanced cervical cancer. Beta-hCG and alpha-fetoprotein have proved to be useful markers for ovarian germ cell tumors. In addition, beta-hCG serves as an ideal tumor marker for monitoring gestational trophoblastic disease and has set the standard with which other assays must be compared.
Studies aimed at improving the detection of epithelial ovarian cancers, especially at an early stage, have identified several new candidates for markers. These include lysophosphatidic acid (a lipid found in serum and ascitic fluid), mesothelin, HE4, osteopontin, VEGF, IL-8, M-CSF, and different kallikreins.
Among these potential markers, HE4 has sensitivity similar to CA-125 in detecting late-stage disease and greater specificity than CA-125 in detecting early ovarian cancer. Validation of HE4 as a diagnostic biomarker for early-stage ovarian cancer is ongoing. New approaches to facilitate identification of novel markers that may be altered early in disease include high-throughput techniques using microarray technology and proteomic screening.
To distinguish porocarcinoma from squamous cell carcinoma, cytokeratin 19 can be a helpful marker. A study by Mahalingam et al found diagnostic sensitivity and specificity to be improved using a selected panel of immunohistochemical stains that includes cytokeratin 7, cytokeratin 19, and nestin. 
For more information, see Ovarian Cancer.
Cancer Antigen 125
Approximately 90% of ovarian cancers are celomic epithelial carcinomas and contain a celomic epithelium–related glycoprotein, designated cancer (or carcinoma) antigen 125. CA-125 can be localized in most serous, endometrioid, and clear cell ovarian carcinomas; mucinous tumors express this antigen less frequently.
Since its discovery in the early 1980s, CA-125 has proven to be a useful first-generation marker for monitoring ovarian cancer and triaging patients with pelvic masses, despite limitations in sensitivity and specificity. False-positive results may derive from several conditions, especially those associated with peritoneal inflammation, such as endometriosis, adenomyosis, pelvic inflammatory disease, menstruation, uterine fibroids, or benign cysts.
CA-125 values may also be elevated in a number of gynecologic (eg, endometrium, fallopian tube) and nongynecologic (eg, pancreas, breast, colon, lung) cancers. However, the most marked elevations (>1500 U/mL) are generally seen with ovarian cancer.
Significant predictive factors for the presence of malignant transformation of endometriosis appear to include age older than 49 years and cysts that are multilocular and have solid components.  Although elevated, levels of serum CA-125 do not appear to be a significant predictor of malignant transformation of endometriosis.
The American College of Obstetricians and Gynecologists and Society of Gynecologic Oncologists guidelines for referring patients to a gynecologic oncologist recommend referral for women with a pelvic mass suggestive of ovarian cancer and a serum CA-125 value higher than 35 U/mL in postmenopausal women or higher than 200 U/mL in premenopausal women.
Applications in ovarian cancer detection
Early detection of ovarian cancer through the measurement of CA-125, usually in combination with other modalities (eg, bimanual pelvic examination, transvaginal ultrasonography), is the most promising application of this tumor marker, permitting effective triage of patients for primary surgery. 
An algorithm has been developed that estimates the risk of ovarian cancer based on the level and trend of CA-125 values. In addition, several trials are ongoing to determine the potential of CA-125 in combination with other markers to increase earlier detection of occult ovarian cancer.
Detection of recurrence and progression of ovarian cancer
The predominant use of CA-125 is in monitoring the status of patients with known ovarian cancer. Persistent elevation of serum CA-125 has generally reflected persistence of disease at second-look surveillance procedures. However, residual disease can be found at laparoscopy or laparotomy, despite a serum CA-125 value that has returned to within normal limits.
An increase in the serum CA-125 value during or after treatment is a strong predictor of future disease progression. A rapid decrease in the CA-125 value during initial treatment correlates with longer progression-free intervals and survival. A serum CA-125 value of less than 15 U/mL after a standard 6-course treatment generally correlates with longer progression-free intervals, although it does not predict whether microscopic disease is present. A CA-125 value greater than 35 U/mL after a standard 6-course chemotherapy treatment predicts the presence of disease. Disease may also progress when CA-125 values are stable.
The Gynecologic Cancer Intergroup uses the Rustin definition to define a rise in CA-125. If the CA-125 value becomes normal after surgery, a subsequent level twice the upper limit of normal is consistent with progression. If the CA-125 value is not normal after surgery, then a subsequent level twice the patient's nadir value indicates progressive disease.
Kang et al found that the nadir level of CA-125 is an independent prognostic factor in patients with advanced epithelial ovarian cancer. In a retrospective review of 153 patients, the median progression-free survival was 32.4 months in patients with nadir CA-125 values of less than or equal to 10 U/mL versus 16.8 months in those with a nadir of 0-35 U/mL (P = .0001). The authors note that whether maximal surgical debulking can affect nadir CA-125 levels remains unclear. 
Standardized CA-125 values have the potential to complement or, in some cases, replace current therapeutic response criteria in a cost-effective way. Rising CA-125 values may precede clinical detection of recurrent disease by at least 3 months. Given the modest efficacy of salvage chemotherapy, this information has not yet influenced survival rates. Rising CA-125 levels during subsequent chemotherapy is associated with progressive disease in at least 90% of cases. CA-125 may serve as an effective surrogate marker for clinical response in clinical trials of new drugs.
Ovarian cancer screening using CA-125
Currently, ovarian cancer screening is not recommended for women with no risk factors (relative risk [RR] ≤3). For women at increased risk (RR = 3-6 times), after evaluating risks and benefits, ovarian cancer screening with CA-125 measurement and/or transvaginal ultrasonography may be considered, usually by way of a clinical trial. 
Women at high risk (RR >6 times), such as those with mutations in ovarian cancer susceptibility genes, should be screened by a combination of transvaginal ultrasonography and CA-125 measurement. [7, 10] For patients with mutations in BRCA1 or the mismatch repair genes, MLH1, MSH2, and MSH6, screening should begin around age 30-35 years. For patients with mutations in BRCA2, ovarian cancer screening should be performed beginning around age 35-40 years.
Early-stage ovarian cancer has an excellent prognosis after definitive therapy. Therefore, early detection is vital in reducing mortality due to this disease. However, no general screening program for ovarian cancer has achieved this goal. Several studies have been launched to identify the best strategy for detecting early stage disease and reducing mortality by using either CA-125 or ultrasonography as the primary screening test.
High specificity is important in screening strategies for ovarian cancer, because a positive test result generally requires definitive surgical assessment. Given the relatively low prevalence of ovarian cancer, a test with 95% specificity would result in 50 surgical procedures for every ovarian cancer detected.
Einhorn and colleagues screened 5550 women with CA-125 alone and found an unacceptable rate of 29 surgeries for every cancer detected. 
Another major limitation of CA-125 screening is that serum levels are elevated in only approximately 50% of patients with stage I disease.
Because other conditions can elevate CA-125 values, combination test strategies have been attempted to improve the predictive value of CA-125.
Jacobs et al were able to show a median survival benefit to the use of a combination of CA-125 levels and ultrasonographic imaging for the detection of ovarian cancer. The investigators randomized 22,000 postmenopausal women to screening with 3 annual CA-125 measurements or no screening. 
Patients in the screened group who had a CA-125 value higher than 30 U/mL underwent transvaginal ultrasonography. Twenty-nine women were referred for surgical exploration, and 6 women were diagnosed as having ovarian cancer (3 of whom had stage I disease). The positive predictive value was 20.7%. Ten additional women in the screening arm developed ovarian cancer during follow-up. Twenty women in the control arm developed ovarian cancer. The investigators were able to show a median survival benefit to screening (72.9 mo in the screened arm vs 41.8 mo in the control group). 
Beta Human Chorionic Gonadotropin
The beta subunit of human chorionic gonadotropin (beta-hCG) is normally produced by the placenta. Elevated b-hCG levels are most commonly associated with pregnancy; false-positive elevations occur in hypogonadal states and with marijuana use. Beta-hCG is degraded to the beta-core fragment, which is concentrated in urine and is also known as urinary gonadotropin peptide. Urinary gonadotropin fragment and lipid-associated sialic acid are elevated in up to 60% of patients with endometrial cancer.
Elevations in beta-hCG are also found in patients with choriocarcinoma of the uterus, embryonal carcinomas, polyembryomas, mixed cell tumors, and, less commonly, dysgerminomas.
Beta-hCG and human placental lactogen (hPL) are the most useful markers for trophoblastic disease and can be localized in syncytiotrophoblasts of partial and complete hydatidiform moles. The intensity and pattern of immunoreactivity for these antigens differ in partial and complete moles. Gestational choriocarcinomas demonstrate variable, but positive, staining for beta-hCG and hPL. The hPL immunostaining differentiates placental-site trophoblastic tumors from choriocarcinomas. The use of beta-hCG is not limited to trophoblastic diseases; it has been found in a wide array of nontrophoblastic gynecologic neoplasms.
The following diagnostic criteria are commonly used for malignant gestational trophoblastic disease:
Plateauing of beta-hCG levels over at least 3 weeks
Ten percent or greater rise in beta-hCG for 3 or more values over at least 2 weeks
Persistence of beta-hCG 6 months after molar evacuation
Histologic identification of choriocarcinoma
Patients who have undergone molar pregnancy evacuation should have weekly beta-hCG monitoring until normal levels are achieved, then monthly monitoring until 6-12 months of normal values have been achieved. Approximately 20% of patients undergoing evacuation of molar pregnancy develop postmolar gestational trophoblastic disease, usually manifesting as failure to normalize the postevacuation beta-hCG levels. A 10% rise in beta-hCG over 3 or more weekly titers or a beta-hCG titer of 40,000 mIU/L 4-5 months after uterine evacuation constitutes a serological diagnosis of postmolar trophoblastic disease.
For metastatic malignant trophoblastic disease, beta-hCG monitoring is recommended every 6 months indefinitely, because late recurrence is a possibility.
Alpha-fetoprotein (AFP) is a normal fetal serum protein synthesized by the liver, yolk sac, and gastrointestinal tract. It shares sequence homology with albumin. AFP is a major component of fetal plasma, reaching a peak concentration of 3 mg/mL at 12 weeks of gestation. Following birth, AFP rapidly clears from the circulation, because its half-life is 3.5 days. AFP concentration in adult serum is less than 20 ng/mL.
Most endodermal sinus tumors of the ovary express AFP. It is present in the cytoplasm of tumor cells and in the characteristic hyalin globules observed in the endodermal sinus tumor. AFP is also expressed by ovarian embryonal cell carcinoma, immature teratomas, and polyembryomas.
AFP and beta-hCG play crucial roles in the management of patients with nonseminomatous germ cell tumors. AFP or beta-hCG is elevated in 85% of patients with these tumors but in only 20% of patients with stage I disease. Hence, these markers have no role in screening.
In patients with extragonadal disease or metastasis at the time of diagnosis, highly elevated AFP or beta-hCG values can be used in place of biopsy to establish a diagnosis of nonseminomatous germ cell tumor.
AFP values in excess of 10,000 ng/mL or beta-hCG levels greater than 50,000 mIU/mL at initial diagnosis portend a poor prognosis, with a 5-year survival rate of 50%. Similarly staged patients with lower AFP and beta-hCG levels have a cure rate of greater than 90%.
Following AFP and beta-hCG levels is imperative in monitoring response to treatment in patients who have nonseminomatous germ cell tumors. Patients with AFP and beta-hCG levels that do not decline as expected after treatment have a significantly worse prognosis, and changes in therapy should be considered. Because curative salvage therapy is possible, the tumor markers are followed every 1-2 months for 1 year after treatment, then quarterly for 1 year, and less frequently thereafter.
AFP or beta-hCG elevation is frequently the first evidence of germ cell tumor recurrence; a confirmed elevation should prompt reinstitution of therapy.
In spite of complete clinical response after chemotherapy, almost 50% of patients with stage III/IV disease have residual tumor. Among patients with persistent elevation of CA-125, approximately 90-95% have residual tumor. The beta-hCG level is used for monitoring response to therapy and detecting early relapse. Testing for beta-hCG is an integral part of diagnosis, management, and response to treatment for gestational trophoblastic disease and in selected patients with epithelial carcinomas of the ovary.
Combined AFP and beta-hCG testing is an essential adjunct in the evaluation and treatment of nonseminomatous germ cell tumors, and in monitoring the response to therapy. AFP and beta-hCG may also be useful in evaluating potential origins of poorly differentiated metastatic cancer. 
Inhibin is a peptide hormone normally produced by ovarian granulosa cells. It inhibits the secretion of follicle-stimulating hormone (FSH) by the anterior pituitary gland. It reaches a peak of 772 ± 38 U/L in the follicular phase of the menstrual cycle; it usually becomes nondetectable after menopause. Certain ovarian tumors, mostly mucinous epithelial ovarian carcinomas and granulosa cell tumors, also produce inhibin, and its serum levels reflect the tumor burden.
An elevated inhibin level in a postmenopausal woman or a premenopausal woman presenting with amenorrhea and infertility is suggestive of, but not specific for, the presence of a granulosa cell tumor. Inhibin levels can also be used for tumor surveillance after treatment to assess for residual or recurrent disease.
Inhibin exists in 2 different isoforms, inhibin A and inhibin B. Both isoforms consist of a dimer of 2 subunits, the alpha and beta subunits. The alpha subunit is the same for both isoforms, while the beta subunits differ (beta A and beta B) and show approximately 64% homology. The 3 subunits (alpha, beta A, beta B) are produced on separate genes, which are located on chromosomes 2 (alpha and beta B) and 7 (beta A).
Although most commercial laboratories provide assays for inhibin A only, serum levels of inhibin B seem to be elevated more frequently. Whenever available, assays to detect both isoforms are recommended. The free alpha subunit can also be measured.
The availability of markers of ovarian stroma, including melan-A and inhibin-alpha, has provided a means for the positive identification of ovarian stromal tumors, which can manifest myriad histological appearances.
Other Tumor Markers
Estradiol was one of the first markers identified in the serum of patients with granulosa cell tumors. In general, estradiol is not a sensitive marker for granulosa cell tumors. Approximately 30% of tumors do not produce estradiol, because they lack theca cells, which produce androstenedione, a necessary precursor for estradiol synthesis. However, monitoring serum estradiol postoperatively may be useful for detecting recurrence of an estradiol-secreting tumor.
Most vulvar tumors of sweat gland origin, including malignant tumors, stain positively for carcinoembryonic antigen (CEA). In most instances, staining for CEA occurs in cells that line cysts, form glands, or are arranged around a lumen. The reaction for CEA does not differentiate eccrine from apocrine adnexal tumors.
In patients with vaginal adenosis, surface columnar epithelium and glands may show focal cytoplasmic membrane staining for CEA. As the columnar cells are gradually replaced by the process of squamous metaplasia, CEA positivity may be observed in the cytoplasm of metaplastic cells.
In situ and invasive adenocarcinomas underlying extramammary Paget disease of the anogenital area express CEA. CEA is also demonstrable in Paget cells at metastatic sites, such as lymph nodes. CEA is present in most urothelial adenocarcinomas of the female urethra.
CEA levels are elevated in up to 35% of patients with endometrial cancer. CEA immunohistochemistry cannot distinguish between benign and malignant glandular proliferations of the uterine cervix; therefore, CEA staining is of no value in the differential diagnosis of endocervical and endometrial adenocarcinomas.
Most epithelial neoplasms of the ovary also express CEA. The neoplasms include, with decreasing intensity and frequency, Brenner, endometrioid, clear cell, and serous tumors.
CEA is frequently present in patients with cancer that has metastasized to the ovary; that is because the primary cancer is generally mammary or gastrointestinal in origin, and such tumors frequently contain CEA.
Squamous cell carcinoma antigen
Squamous cell carcinoma (SCC) antigen may be increased in patients with epidermoid carcinoma of the cervix, benign tumors of epithelial origin, and benign skin disorders. SCC antigen may be helpful in assessing response to chemotherapy and in determining relapse when monitoring patients with complete remission.
Müllerian inhibiting substance
Müllerian inhibiting substance (MIS) is produced by granulosa cells in developing follicles. It has emerged as a potential tumor marker for granulosa cell tumors. As with inhibin, MIS is typically undetectable in postmenopausal women. An elevated MIS value is highly specific for ovarian granulosa cell tumors; however, this test is not commercially available for clinical use.
Topoisomerase II has emerged as a promising, clinically relevant biomarker for survival in patients with advanced epithelial ovarian cancer. Its expression is detected in tumor samples by immunohistochemistry.
Carbohydrate antigen 19-9
Serum carbohydrate antigen 19-9 is elevated in up to 35% of patients with endometrial cancer and can be used in the follow-up evaluation of patients with mucinous borderline ovarian tumors.
Measurement of serum tumor markers in the follow-up care of these patients may lead to earlier detection of recurrence in only a very small proportion of patients; the clinical value of earlier detection of recurrence remains to be established. Carbohydrate antigen is not specific for ovarian cancer.
Cancer antigen 27-29
Elevated cancer antigen 27-29 levels are associated with cancers of the colon, stomach, kidney, lung, ovary, pancreas, uterus, and liver. First-trimester pregnancy, endometriosis, ovarian cysts, benign breast disease, kidney disease, and liver disease are noncancerous conditions that are also associated with increased cancer antigen 27-29.
Human telomerase reverse transcriptase
Human telomerase reverse transcriptase (hTERT) is a novel biomarker for patients with ovarian and uterine cancers. The hTERT mRNA level has a significant correlation with CA-125 and with histologic findings in ovarian cancer. 
Serum hTERT mRNA is useful for diagnosing gynecologic cancer and is superior to conventional tumor markers. Up-regulation of hTERT may play an important role in the development of cervical intraepithelial neoplasia (CIN) and cervical cancer; hTERT could be used as an early diagnostic biomarker for cervical cancer in the future.
Lysophosphatidic acid stimulates cancer cell proliferation, intracellular calcium release, and tyrosine phosphorylation, including mitogen-activated protein kinase activation. Lysophosphatidic acid has been shown to be a multifunctional signaling molecule in fibroblasts and other cells. It has been found in the ascitic fluid of patients with ovarian cancer and is associated with ovarian cancer cell proliferation. Further studies are needed to determine the role of this marker.
MIB1-determined tumor growth fraction
MIB1-determined tumor growth fraction has been studied as an additional tool to aid decisions on adjuvant therapy in patients whose ovarian carcinoma is in a very early stage. In one study, MIB1 predicted tumor recurrences in 84% of the ovarian cancers. 
L1 (CAM), a transmembrane protein, is a novel diagnostic marker in serous ovarian neoplasms that show characteristics of tumor progression. L1 (CAM) expression is associated with chemotherapy response.
According to Daponte et al, immunoreactivity to L1 (CAM) correlates with stage and grade of ovarian cancer. Immunoreactivity increases progressively and significantly from benign tumors to early carcinomas and to advanced stage carcinomas.