Several serum tumor markers have been investigated in patients with breast cancer for assessing outcome, predicting recurrence and monitoring the therapeutic response. There is a general consensus concerning their limited application in diagnosing malignancy; however, serum tumor markers can be considered for the early detection of recurrence. The most effective markers for this indication are cancer antigens (CA)15-3 and 27.29, and c-erbB-2, although their efficacy in establishing disease progression has not been determined to date. In terms of evaluating prognosis and predicting response to therapy, only the expression of c-erbB-2 has clinical evidence. To conclude, at present, no serum tumor marker is cost effective, and none can be used with confidence in the decision making regarding breast cancer patients.