Discordance in HER2 gene amplification in circulating and disseminated tumor cells in patients with operable breast cancer

Abstract

Human epidermal growth factor receptor 2 ( HER2 ) gene amplification in circulating tumor cells ( CTCs ) and disseminated tumor cells ( DTCs ) might be useful for modifying Herceptin therapy in breast cancer. In the process of investigating the utility of a microfluidic platform for detecting HER2 gene amplification in these cells, we observed novel results on discordance of HER2 status. Peripheral blood (8.5 mL) and bone marrow ( BM ) (7.5–10 mL) were collected prospectively from patients with clinical stages I–IV breast cancer. Mononuclear cells were recovered, stained with cytokeratin ( CK ), CD 45, and DAPI , and processed through microfluidic channels for fluorescence in situ hybridization ( FISH ). A ratio of HER2 : CEP 17 >2 in any CK +/ CD 45 or CK −/ CD 45 cell was regarded as positive for HER2 gene amplification. Peripheral blood from 95 patients and BM from 78 patients were studied. We found CK +/ CD 45−/ DAPI + CTCs in 27.3% of patients. We evaluated HER2 gene amplification by FISH in 88 blood and 78 BM specimens and found HER2 + CTCs in 1 of 9 (11.1%) and HER2 + DTCs (27.2%) in 3 of 11 patients with HER2 + primary tumor. Among patients with a HER2 − primary tumor, 5 of 79 had HER2 + CTCs (6.3%) and 14 of 67 had HER2 + DTCs (20.8%). The overall rate of discordance in HER2 status was 15% between primary tumor and CTCs and 28.2% between primary tumor and DTCs . HER2 was amplified in CTCs and DTCs in a portion of both HER2 + and HER2 − primary tumors. HER2 discordance was more frequent for DTCs . The clinical implications of evaluating HER2 status in CTCs and DTCs in breast cancer needs to be established in prospective clinical trials. The cell enrichment and extraction microfluidic technology provides a sensitive platform for evaluation of HER2 gene amplification in CTCs and DTCs .