Measures of CEA levels in breast cancer, primary or metastatic, have a sensitivity of about 60% and a specificity around 80% for the presence of active disease. In other words, there's a 40% chance of a false negative test and 20% chance of a false positive result. This renders the test essentially useless to screen for primary or recurrent breast cancer and is an unreliable marker for keeping tabs on treatment of the disease. In fact, there's no clinically valuable serum tumour marker available for breast cancer available to date. JJ