CA 125 as a Serum Tumour Marker

CA 125 (cancer antigen 125) is a glycoprotein derived from coelomic epithelium. Although it is best known as a tumour marker for epithelial ovarian cancer, it is a non-specific marker that is elevated in a wide range of benign and malignant conditions involving irritation or inflammation of the peritoneal and pelvic mesothelial surfaces.

Analysis of Each Condition

• 1. Epithelial ovarian cancer: CA 125 is the standard tumour marker used for diagnosis, monitoring response to treatment, and detecting recurrence in epithelial ovarian carcinoma. Levels are markedly elevated in the majority of cases, especially advanced-stage disease.
• 2. Endometriosis: Ectopic endometrial tissue causes local peritoneal inflammation and irritation, which raises serum CA 125, particularly in moderate to severe disease. It is a well-recognised (though non-specific) marker used to support the diagnosis and monitor endometriosis.
• 3. Pelvic inflammatory disease (PID): Active pelvic and peritoneal inflammation in PID also elevates CA 125. This is a well-documented cause of a raised CA 125 and is one of the classic "benign" conditions (along with fibroids, menstruation, pregnancy, and other causes of peritoneal irritation) that produce false-positive elevations when CA 125 is used to screen for ovarian malignancy.

Why the Other Options Are Incorrect

• 2 and 3 only: Incorrectly excludes epithelial ovarian cancer, which is in fact the condition most strongly and classically associated with a raised CA 125.
• 1 and 3 only: Incorrectly excludes endometriosis, despite it being a well-established benign cause of CA 125 elevation.
• 1 and 2 only: Incorrectly excludes pelvic inflammatory disease, which also causes CA 125 elevation due to associated pelvic/peritoneal inflammation.

Conclusion

Since epithelial ovarian cancer, endometriosis, and pelvic inflammatory disease can all raise serum CA 125, the correct answer is 1, 2 and 3.