Hello, I have been diagnosed with LABC -- locally advanced breast cancer (Stage 3C) I would like to know more about the tumour markers CA 15-3 ,CA 27-29 and CEA. I would like to know how many breast cancer cells must exist in the body to elicit a positive response --- 1, 5, 20 or a few hundred. If a single breast cancer cell can elicit a positive tumour marker response then these tests can be used after treatment (chemo, surgery and radiation) to see if any cancer cell has survived. Alternatively after treatment I can get my blood tested every two weeks to see if there is any recurrence. In other words I am looking for information about the SENSITIVITY of these tumour marker tests. Waiting for your reply (Female, 40 years)