Value of CA 15.3 in breast cancer and comparison with CEA and TPA: a study of specificity in disease-free follow-up patients and sensitivity in patients at diagnosis of the first metastasis.

The specificity and sensitivity of a tumor marker (TM) are important in establishing its potential clinical utility for a specific type of neoplasm. CA 15.3 is a TM specific for breast cancer; it is defined by two monoclonal antibodies (DF3 and 115D8), whose specificity, in disease-free follow-up patients, and sensitivity, in patients at diagnosis of first metastasis, have been evaluated in the present study and compared with those of carcinoembryonic antigen (CEA) and tissue polypeptide antigen (TPA). Serum concentrations of all three TMs were quantified in 618 individuals: 80 healthy controls, 421 patients with local breast cancer who became free of disease following locoregional treatment, and 117 patients with disseminated disease at diagnosis of metastasis. Radioimmunoassay (RIA) was the method employed, and the cut-off values obtained were 30 U/ml for CA 15.3, 5 ng/ml for CEA, and 120 U/I for TPA. The results showed CA 15.3 and CEA specificities to be analogous (95.7 and 95.5%, respectively). TPA specificity (81.9%) was lower (p < 0.001). During adjuvant therapy, CA 15.3 serum levels were seen to increase, followed by a normalization of concentration after terminating therapy. On the other hand, CA 15.3 and TPA sensitivities (64.1 and 67.5%, respectively) were greater than for CEA (44.4%, p < 0.01). It is concluded that CA 15.3 is a useful TM for breast cancer, as it offers a greater sensitivity than CEA and a higher specificity than TPA. Combining CA 15.3 and CEA fails to increase CA 15.3 sensitivity, while combining CA 15.3 with TPA increases false-positives and so likewise offers no additional benefit.