Serum Markers
The most useful serum markers in breast cancer are CA 15-3 (BR 27.29) and carcinoembryonic antigens (CEAs). As mentioned above, serum markers are mainly used in surveillance following surgical resection of the primary cancer and monitoring therapy when patients develop recurrent or metastatic disease. For both these applications, serial determinations of marker(s) are necessary.

Postoperative Surveillance
Approximately 25% of patients with surgically outcome. Indeed, studies carried out over 10 years ago concluded that intensive follow-up of breast cancer patients did not benefit them compared with minimal follow-up. These old studies had a number of limitations, including:

• use of older and less sensitive biochemical tests, such as alkaline phosphatase, aspartate transaminase, gamma glutamyl transferase, bilirubin, calcium and creatinne, rather than the newer tumour markers such as CA 15-3 and CEA; 
• use of older radiological procedures rather than newer procedures such as computed tomography (CT), magnetic resonance imaging (MRI) and positron emission tomography (PET) scanning; and
• most of the reports comparing outcome in control and intensively followed-up patients predate the availability of new treatments for recurrent/metastatic breast cancer such as the taxanes, the new generation of aromatase inhibitors and Herceptin.

The relevance of these older studies to the modern management of breast cancer is thus unclear.
According to the European Group on Tumour Marker (EGTM) Guidelines, serial CA15-3 and CEA determinations are recommended for the early detection of recurrence in asymptomatic patients who had undergone curative surgery for primary breast cancer, if the detection of recurrent or metastatic disease would alter clinical management. Other expert panels such as the American Society of Clinical Oncology (ASCO), however, do not recommend routine use of tumour markers in the post-operative surveillance of newly diagnosed breast cancer patients.