CA‐549: A new tumor marker for patients with advanced breast cancer

A murine monoclonal antibody, BC4E 549, an IgG₁ adapted as tracer antibody in a sandwich immunoradiometric assay, was used to detect a circulating breast cancer‐associated antigen, CA‐549, in patients with advanced breast cancer. The study was designed to examine the specificity and sensitivity of CA‐549 measurements as a specific circulating marker for breast cancer. In a population of 100 normal pre‐and postmenopausal women, serum levels ranged from 1–10 μ/ml. In contrast, 38 of 46 patients (83%) with active, advanced‐stage breast cancer had circulating levels in excess of 10 μ/ml, and levels in several patients exceeded 100 μ/ml. Patients on adjuvant therapy with breast cancer in remission, patients with benign breast disease, and patients with cancers of other sites such as colorectal, ovarian, and lung cancer did not show significant elevations (>10 μ/ml, P > 0.001) of this circulating antigen. Measurement of this breast cancer associated antigen may be of use in the evaluation of treatment for patients with advanced stage breast cancer.