Cancer Antigen-125 (CA-125), Serum

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Subject: Cancer Antigen-125 (CA-125), Serum

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Definition

  • CA-125 is a large glycoprotein (200–1,000 kDa) found on the surface of many ovarian cancer cells and in some normal tissues. It is a product of the MUC16 gene.

  • Normal range: 0–35 U/mL.

Use

  • CA-125 is recommended, together with transvaginal ultrasound, for early detection of ovarian cancer in women with hereditary syndromes because early intervention may be beneficial in these women. It is also recommended as an adjunct in distinguishing benign from malignant suspicious pelvic masses, particularly in postmenopausal women.

  • It is not suggested for screening asymptomatic women.

  • Measurements may also be used to monitor response to chemotherapeutic response.

Interpretation

Increased Values

  • Malignant disease

    • Fallopian tube tumors (100%), nonmucinous epithelial ovarian carcinoma (85%), cervical adenocarcinoma (83%), endometrial adenocarcinoma (50%), and squamous cell carcinomas of vulva or cervix (<15%)

    • Trophoblastic tumors (45%)

    • Non-Hodgkin lymphoma (40%) with pleuropericardial or peritoneal involvement

    • Cancers of the pancreas, liver, and lung

  • Conditions that affect the endometrium

    • Pregnancy (27%)

    • Menstruation, endometriosis

  • Pleural effusion or inflammation (e.g., cancer, congestive heart failure)

  • Peritoneal effusion or inflammation (e.g., pelvic inflammatory disease) and especially in bacterial peritonitis in which the ascitic concentration is greater than the serum concentration

  • Some nonmalignant conditions

    • Cirrhosis, severe liver necrosis (66%)

    • Other diseases and disorders of the GI tract, liver, and pancreas

    • Renal failure

  • Healthy persons (1%)

Decreased Values

  • Postmenopausal women

  • African American and Asian women, for whom normal values are lower

Limitations

  • Human antimurine or heterophile antibodies.

  • The CA-125 level is not increased in mucinous adenocarcinoma.

  • Different assays do not produce equivalent values and should not be used interchangeably.

  • Most of the commercially available assays quote the upper reference limit of 35 IU/mL; some studies have shown that the detection of disease can be significantly improved by lowering the cutoff value.

  • Normal concentration of CA-125 does not exclude tumor.

  • CA-125 is not useful for distinguishing benign from malignant pelvic masses, even at high concentrations.

  • Although CA-125 may be increased ≤12 months before clinical evidence of disease, it is not recommended for screening women for serous carcinoma of the ovary because it is not increased in 20% of cases at the time of diagnosis and in <10% of stage I and II cases (low sensitivity and specificity; high false-positive rate).

    • There is little benefit to early detection of late-stage cancers.

  • Postoperative monitoring for persistent or recurrent disease; poorer prognosis if elevated 3–6 weeks after surgery.

    • Lower levels in patients with no residual tumor or <2 cm of residual tumor.

    • Concentration >35 U/mL detects residual cancer in 95% of patients, but a negative test does not exclude residual disease.

  • Rising level of CA-125 during chemotherapy is associated with tumor progression, and fall to normal is associated with response. It remains elevated in stable or progressive serous carcinoma of the ovary.

  • Rising concentrations may precede clinical recurrence by many months and may be indication for second-look operation, but lack of increased values does not indicate the absence of persistent or recurrent tumor.

  • Greater concentration is roughly related to poorer survival; >35 U/mL is highly predictive of tumor recurrence.

    • With values >65 U/mL, 90% of women have cancer involving the peritoneum.

    • Higher levels are also seen in serous cystadenocarcinoma.

  • Sequential determinations are more useful than a single test, because levels in benign disease do not show significant change but progressive rise occurs in malignant disease.

  • CA-125 is positive in 80% of cases of common epithelial tumors (50% of early-stage disease). It should be noted that 0.6% of normal women older than 50 years of age have increased levels of CA-125.

  • Prognosis may be better if

    • There is a 50% decline in concentration within 5 days after surgery.

    • A postoperative-to-preoperative concentration ratio of 0.1 generally occurs within 4 weeks.

    • People with a postoperative-to-preoperative concentration ratio of >0.1 to <0.5 may benefit from chemotherapy, but the recurrence rate is high.

    • Patients with a postoperative-to-preoperative concentration ratio of >0.8 should consider alternative therapy (e.g., radiation, different chemotherapy combinations).

Suggested Reading

Fritsche  HA, Bast  RC. CA 125 in ovarian cancer: advances and controversy. Clin Chem.  1998;44:1379–1380.
 
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