CA15-3: its relationship to clinical stage and progression to metastatic disease in breast cancer.

There is increasing interest in the potential role of monoclonal antibodies as tumour markers in the early detection of metastatic disease. CA15-3 is a circulating antigen which is relatively specific for breast tissue and defined by two monoclonal antibodies. It is elevated in the serum of patients with breast cancer but its relationship to clinical stage and tumour progression has not been well defined. CA15-3 levels have been measured in a consecutive series of 97 patients with breast cancer at the time of diagnosis and at 3-monthly intervals thereafter. All patients have been evaluated and followed by using routine biochemical and radiological parameters to detect occult metastatic disease. There was no difference between a control group of patients who presented with benign disease (n = 18: means(s.d.) 18.0(5.1) units/ml): and those who presented with stage I disease (n = 37: 18.4(5.3) units/ml) or stage II disease (n =21: 18.0(4.0) units/ml). Patients with stage III disease (n = 23: 32.0(10.4) units/ml) had significantly elevated levels of CA15-3 compared with those in stage I (P less than 0.001). All patients with documented metastatic disease at presentation or at follow-up had markedly elevated CA15-3 levels (n = 10: 155.8(50.2) units/ml). CA15-3 is a reliable tumour marker in patients with advanced disease.