HER-2/neu determination in blood plasma of patients with HER-2/neu overexpressing metastasized breast cancer: a longitudinal study.

This retrospective study was designed to evaluate the serological HER-2/neu determination as a predictor of the clinical outcome of patients with metastasized breast cancer receiving a trastuzumab therapy. Twenty trastuzumab patients were included into this study. Plasma samples of each patient were collected from the beginning of a trastuzumab therapy until the first imaging diagnostics. Serological HER-2/neu was quantified automatically using the Bayer Immuno 1 immunoanalyzer. Each assay was performed in duplicate. The values were analyzed in terms of the clinical course of each patient. The observation time was 13 months (median) with a range from 4 to 22 months. The data were analyzed by means of prediction of a therapy response as defined by the time to progression. HER-2/neu determination served as a predictive marker for the clinical course in 16 out of 20 patients (80%). All ten therapy responders displayed a normal HER-2/neu either from the beginning of the trastuzumab administration or a value normalization paralleled the course. Patients with permanent elevated or increasing HER-2/neu levels displayed a poor clinical outcome in six out of ten cases. Our data suggest that HER-2/neu determination in the plasma of patients with metastasized breast cancer could be a powerful tool for prediction of the patient's outcome after a trastuzumab-based therapy.