Abstract P3-02-13: Is HER2 Evaluation with the CellSearch System a Method Reliable for Detecting HER2 Overexpression?
Authors: Sandri MT , Zorzino L , Cassatella MC , Dell'Orto P , Stufano V , Munzone E , Casadio C. 
Published: April 2011

Background. Circulating tumor cells (CTCs) detected in patients with both localized and metastatic breast cancer are significantly associated with a worse outcome. In addition to enumeration, an exciting area of CTC research involves the phenotyping and expression profiling of CTCs. In this regard, in patients with metastatic breast cancer, the evaluation of CTCs could be considered as a “real-time” biopsy allowing the detection of possible changes in tumor phenotype, such as a shift in patients HER2- negative on the primary tumor to HER2-positive CTCs. This could be of relevance as these patients may become suitable to targeted anti-HER2 therapy. Currently, there is no standardized and widely accepted method available for the determination of HER2 status on CTC. Aims. Objectives of this study were: 1. verifying the feasibility and reliability of HER2 determination on cells from scraping of breast cancer tissue by FISH analysis, 2. evaluating the concordance of HER2 status determined on primary breast tumor by immunohistochemistry (IHC) and on scraped cells, obtained from the same breast tumor and spiked in blood from healthy subjects, using the CellSearch System, and finally 3. evaluating the concordance of HER2 expression determinated by FISH analysis and by CellSearch on the same scraped cells. Methods. Cells from scraping of fresh breast cancer tissues with different level of HER2 expression were spiked in 18 healthy subjects blood samples. The determination of the HER2 expression on these cells was performed with the CellSearch System (Veridex, USA) by the addition of a fluorescein conjugated monoclonal antibody to be used in conjunction with the CellSearch™ Epithelial Cell Kit to phenotype CTCs for the presence of HER-2/neu. The HER2 characterisation of the primary breast tumors was performed by IHC by FISH analysis according to standard procedures. FISH was also performed on cells from scraping of fresh breast cancer tissues after CellSearch enumeration and characterization, by removing them from the “MagNest” cartridge. Tumors with a score of 3+ were considered positive.

Results. The results of the FISH analysis performed on the cells aspirated from the cartridge demonstrated a 100% concordance with the FISH performed on fresh tissue (9 not amplified and 9 amplified). The evaluation of HER2 expression on scraped cells by CellSearch System and by IHC on the corresponding tumor showed that the CellSearch method is reliable in identifying HER2 overexpression, as in all the 3+ tumors it was possible to detect variable percentage of scraped cells overexpressing HER2. Finally, different number of HER2+ scraped cells were found in 16 out of the 18 samples: the only 2 negative samples were both IHC negative and FISH not amplified. On the contrary 2 of the 4 remaining negative/1+ IHC samples, showed some scraped cells HER2+ which resulted FISH amplified. Conclusion. This study demonstrates that FISH analysis is feasible and the results are reliable when performed on cells after CellSearch procedure. Moreover HER2 expression may be evaluated with the CellSearch System and it may be used as a preliminary method to indicate possibly HER2 positive samples which may be confirmed by FISH analysis.

Citation Information: Cancer Res 2010;70(24 Suppl):Abstract nr P3-02-13.