CA 15-3

Function

Cancer Antigen 15-3 (CA 15-3) is a protein produced by normal breast cells. However, in many patients with cancerous breast tumors, there is an increased production of CA 15-3 and the related antigen CA 27.29. This protein is shed into the bloodstream, making it a measurable tumor marker in clinical oncology.

Why it is Ordered

CA 15-3 is primarily utilized to monitor the treatment of invasive breast cancer and to watch for recurrence. It is not generally used as a screening tool for early-stage breast cancer because many early-stage cancers do not cause elevated levels, and levels can be high in individuals with non-cancerous conditions. It is most valuable for:

• Monitoring Therapy: Observing the efficacy of chemotherapy or hormonal therapy in advanced breast cancer.
• Recurrence Surveillance: Detecting the return of cancer after successful initial treatment.
• Disease Progression: Gauging the extent of metastatic disease.

Associated Conditions

While most closely linked with breast cancer, elevated CA 15-3 levels are associated with several other conditions:

• Malignant Conditions: Lung, pancreatic, ovarian, and prostate cancers.
• Benign Conditions: Endometriosis, pelvic inflammatory disease, cirrhosis, and benign breast disease.
• Inflammatory States: Certain systemic inflammatory conditions can cause transient elevations.

Clinicians typically use CA 15-3 in conjunction with physical exams, imaging (like mammograms or CT scans), and other laboratory findings to form a complete clinical picture. A declining level usually indicates a positive response to treatment, while a rising level may suggest tumor growth or recurrence.