CA-125

CA-125 (cancer antigen 125) is a protein measured in the blood that can be elevated in several cancers, including ovarian cancer and mesothelioma, as well as in non-cancerous conditions like endometriosis, pleural effusion, and liver disease. It is not a stand-alone diagnostic test, but levels often track with disease activity and can be useful for monitoring response to treatment.

Origin

CA-125 was identified in 1981 by Robert Bast and colleagues at Harvard using a monoclonal antibody (OC125) raised against an ovarian cancer cell line. The protein it detects is encoded by the MUC16 gene and is part of the mucin family of cell-surface glycoproteins.

Significance in Asbestos Context

For patients with pleural or peritoneal mesothelioma, CA-125 is sometimes ordered alongside other markers (such as mesothelin/SMRP) to help follow the disease over time. It is most useful for trend tracking (rising levels may suggest progression, falling levels may suggest treatment is working) rather than for making the initial diagnosis. CA-125 can also be elevated simply because of pleural or peritoneal fluid buildup, so a single high number does not by itself mean cancer or worsening cancer. In medical records, serial CA-125 values can become part of the documentation showing how the disease progressed, which may matter when describing the course of illness in a legal claim.

Example Sentence

"After her peritoneal mesothelioma diagnosis, her oncologist began checking CA-125 every few cycles of chemotherapy to see whether the treatment was working."

Related Terms

Mesothelin (SMRP), Biomarker, Peritoneal Mesothelioma, Pleural Effusion, Tumor Marker, MUC16

Notes

• Ask your oncologist whether CA-125, mesothelin (SMRP), or both should be monitored in your specific case. Practice varies by cancer type and center.
• Keep copies of every CA-125 result with the date; a trend line over months is far more meaningful than any single value.
• Be aware that benign causes (fluid buildup, infection, menstruation, recent surgery, liver disease) can raise CA-125 and do not necessarily mean the cancer is progressing.
• CA-125 should never be used alone to diagnose mesothelioma. Diagnosis requires tissue biopsy with immunohistochemistry.