Preparation
CA 15.3 is a tumour marker associated with breast cancer, used almost exclusively for monitoring rather than diagnosis. Its value is in following women already diagnosed and treated for breast cancer: rising CA 15.3 across repeat tests can flag recurrence before symptoms appear, and falling values confirm that treatment is working.
Used correctly, it is a quiet, powerful tool — one home blood draw every few months instead of repeated hospital visits. Used incorrectly — as a screening test in a healthy person — it creates anxiety, because benign breast conditions can also nudge the value upward.
If you are under treatment or surveillance for breast cancer, ask your oncologist for the monitoring interval they prefer; home collection keeps the readings consistent. Results are released in your app, ready for your treating team.
No. It is neither sensitive nor specific enough for screening — mammography and clinical examination do that job. CA 15.3 is a monitoring tool for those already diagnosed.