Test Background CA 15-3 is a high molecular weight (300-450 kDa) transmembrane glycoprotein encoded by the MUC1 gene. It is defined by reactivity with 2 monoclonal antibodies, DF3 and 115D8. CA 15-3 is expressed predominantly in breast cancer (raised in 30 % of localised disease, 75 % metastatic), though primary tumours of the lung, colon, pancreas, liver and endometrium may also give rise to elevations of CA 15-3. Elevations of CA 15-3 values have been reported in individuals with non-malignant conditions such as cirrhosis, hepatitis, autoimmune disorders and benign diseases of the ovary and breast. While increasing CA 15-3 can be the earliest sign of metastatic disease in ~70 % patients, there is little evidence showing that early diagnosis of progressive disease positively impacts survival or quality of life.
Clinical IndicationsBreast cancer
Diagnosis: since CA 15-3 may be elevated in normal individuals and benign conditions, and there is a low incidence of CA 15-3 elevation in early stage breast cancer, CA 15-3 should not be used for screening.
Treatment monitoring: when serum CA 15-3 level is elevated it may be used to monitor response to therapy in combination with imaging and clinical examination. For patients with metastatic disease in whom CA 15-3 is being monitored, the marker should be determined prior to each chemotherapy course and at 3 month intervals.
Surveillance: despite the lack of high level evidence, many patients opt to have serial levels of CA 15-3 determined following surgery.