HER2+ circulating tumor cells (CTCs): a more sensitive and specific marker for CTCs positivity than total CTCs count in early breast cancer.

Abstract

Abstract Abstract #5023 Background: CTCs have been detected using the CellSearch System in early and metastatic breast cancer (BC). However, no studies have been reported for the detection of HER2+ CTCs using the CellSearch System. In this study we aimed to analyze CTCs for HER2 expression in different stages of BC progression from ductal/lobular carcinoma in situ (DCIS/LCIS) to early and metastatic BC. Patients and Methods: 20ml of peripheral blood per woman was analyzed from healthy women, DCIS/LCIS or early BC patients, whereas 7.5ml of blood was analyzed from metastatic BC patients. The presence of CTCs as well as HER2 expression was assessed with the CellSearchSystem (Veridex, USA). After immunomagnetic enrichment with an anti-Epcam-antibody, cells were labeled with anti-cytokeratin (8,18,19), anti-HER2 and anti-CD45 antibodies. CTCs were defined as Cytokeratin-positive/CD45-negative cells, whereas HER2+ CTCs were defined as Cytokeratin-positive/CD45-negative/HER2-positive cells. Results: The presence of CTCs and HER2+ CTCs in healthy women, DCIS/LCIS, early and metastatic BC is depicted in table.
 
 Since 1 and 2 CTCs were detected in 7 (14.8%) and 4 (8.5%) of 47 healthy women, respectively, >1CTC or >2CTCs were selected as cutoffs for further analysis. Using the above cutoffs, 7 (18.9%) and 5 (13.5%) of 37 patients with early BC were considered CTC-positive, respectively. Since no HER2+ CTCs were detected in any of the 47 healthy women, a cutoff of ≥1 HER2+ CTCs was chosen. With this cutoff, more women with early BC [11 (29.7%) of 37 women] were considered CTC-positive. Conclusion: HER2+ CTCs seems to be a more sensitive and specific marker for CTCs' positivity than total CTCs counts in early breast cancer. Clinical relevance of the above cutoff for CTCs positivity using HER2+ CTCs detection will be performed in ongoing clinical trials of HER2 positive early breast cancer. Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 5023.