Relationship of Serum HER-2/neu and Serum CA 15-3 in Patients with Metastatic Breast Cancer

Serum HER-2/neu antigen concentrations have been reported to correlate with increased tumor volume in patients with breast cancer. We measured serum CA 15-3, a surrogate marker of disease burden, and correlated serum CA 15-3 with serum HER-2/neu and analyzed the association of both markers with clinical outcomes. Pretreatment serum samples from 566 patients were retrospectively analyzed from 2 phase III clinical trials of estrogen receptor-positive (ER(+)), ER(-)/progesterone receptor-positive, or ER status unknown metastatic breast cancer patients randomized in two similar studies to receive second-line hormone therapy with either megestrol acetate or an aromatase inhibitor (fadrozole). The extracellular domain of the HER-2/neu (c-erbB-2) oncogene and serum CA 15-3 were measured by ELISA on the Bayer Immuno 1. Serum HER-2/neu protein was increased in 168 patients (30%), and CA 15-3 was increased in 337 (60%) patients. Serum CA 15-3 and HER-2/neu were weakly correlated (r = 0.39; P