Efficacy control of therapy using circulating epithelial tumor cells (CETC) as “Liquid Biopsy”: trastuzumab in HER2/neu-positive breast carcinoma

PURPOSE: The majority of targeted personalized cancer therapies are effective only in part of the patients, and most of these drugs are excessively expensive. Therefore, methods are urgently required, which reveal already early during treatment, whether the therapy is effective. In the present report, monitoring of circulating epithelial tumor cells (CETC) was used as a timely control of trastuzumab therapy in patients with HER2/neu-positive breast cancer. METHODS: Seventy-nine sequential HER2/neu-positive breast cancer patients, 35 without trastuzumab, and 36 treated with 1 year of trastuzumab treatment were included. CETC from unseparated white blood cells stained with FITC-anti-EpCAM were analyzed repeatedly during chemotherapy and between 2 and 10 times during 1 year of maintenance treatment or observation. RESULTS: Patients treated with trastuzumab had a better relapse-free survival than patients without trastuzumab treatment during the first 2–4 years of follow-up. Decrease in numbers or no change versus highly variable numbers or increase (fivefold or more) allowed to discriminate highly significantly and clearly (P < 0.0001, hazard ratio 5.5) between patients with a low or high risk of relapse. An increase in CETC was accompanied by an increasing portion of cells containing a very high number of HER2/neu gene amplificates. CONCLUSIONS: Analysis of the behavior of CETC can, in the future, contribute to evaluate the efficacy of targeted therapy early during the course of the disease, sparing patients unnecessary treatment but also to reduce the costs for the health system and to downsize the extent and length of clinical studies.