Monitoring expression of HER-2 on circulating epithelial cells in patients with advanced breast cancer

Nineteen breast cancer patients with measurable metastatic disease who were starting an initial or new line of therapy were evaluated for circulating epithelial cells (CECs) a minimum of 4 times over the course of treatment. In 7 of the 10 CEC+ patients, HER-2 expression was detected on the CECs. CECs expressing HER-2 varied among patients and in serial samples from the same patient including a shift from HER-2- to HER-2+ CECs. These results demonstrate that it is possible to quantify receptors essential for rationally designed therapy using CECs and that reliance on the immunophenotype of the primary tumor can be misleading.