The CA 15-3 test measures the level of a protein called cancer antigen 15-3 in your blood. This protein is often elevated in women with breast cancer, though it can also be raised in other conditions, both cancerous and non-cancerous.

Why it’s important:

• Breast cancer monitoring: CA 15-3 is commonly used to monitor breast cancer patients, particularly to check for recurrence or to assess the effectiveness of treatment (such as chemotherapy or hormone therapy).
• Early detection: While not used for screening (it’s not specific enough to detect breast cancer early), elevated CA 15-3 levels may sometimes indicate the presence of cancer, particularly in advanced stages of breast cancer.
• Other conditions: Elevated CA 15-3 can also be found in other cancers (such as ovarian, lung, or liver cancer) or in non-cancerous conditions, such as benign breast disease, liver disease, or chronic inflammatory conditions like endometriosis.