Cancer antigen 125 (CA-125) is a protein typically located on the surface of the ovarian cancer cells, although it can also be encountered on other types of cancerous tumors, as well as in healthy tissues in low concentrations. The blood test can reveal the amount of CA-125 protein within the body, thus proving to be an effective method of both diagnosing and monitoring ovarian cancer.



Additionally, it can be performed along with transvaginal ultrasound on women who are at a higher risk of developing the disease, as well as to determine whether this type of cancer has reappeared in patients who have previously suffered from it. It is important to mention that the CA-125 test may offer highly inaccurate results for younger women, as increased concentrations of the protein can occur due to other conditions such as irritable bowel syndrome, diverticulitis or appendicitis.