Abstract P3-04-01: Manual and digital detection of HER2 status of 2721 circulating tumour cells in patients with metastatic breast cancer
Authors: Brouwer A , van de Wiel M , Peeters B , van Dam P-J , Vermeulen P , Peeters M , Van Laere S , Peeters D , Dirix L 
Published: May 2016

Abstract
Introduction:
In metastatic breast cancer (MBC), discordant expression levels of the human epidermal growth factor receptor 2 (HER2) have been noted between primary tumours (PT) and matched metastatic lesions (Meta). Therefore reassessment of this predictive marker at time of metastatic disease might help to optimize treatment. Circulating tumour cells (CTCs) offer the potential to provide a repeatedly accessible source of tumour cells for the real-time assessment of actual tumour characteristics.
Here we report on a retrospective study analysing over two and a half thousand CTCs in order to evaluate the inter-observer variability when using the semi-quantitative scale (0-3+) described by Riethdorf in 2010. Furthermore we designed a digital scoring system using 13 parameters selected by ImageJ. HER2 status in CTCs was compared to PT and/or Meta of patients with MBC.
Materials and methods:
65 patients starting first or second line systemic therapy for MBC and harbouring more than 5 CTC/7.5 mL blood were selected. HER2 status of 2721 CTCs was determined by immunofluorescence using the CellSearch system. HER2 status of the solid lesions was determined by IHC or FISH. Inter-observer variability was calculated using the Kendalls tau tests. 284 CTCs were analysed with the digital scoring system using ImageJ 'plot profile' and 'analyse particles'. Selected parameters comprise cell size, mean and maximum intensity of the cell and its surrounding, and both ratio's and differences of the aforementioned. Dissimilarity matrix was calculated using Pearson Correlation-Distance.
Results:
Of 2721 CTCs, 1485 cells (55%) were scored 0+ and 2263 cells (83%) were found to be HER2- (0+ or 1+) by both observers. 458 cells (17%) were scored HER2+ (2+ or 3+) by at least one of the observers, however only 175 (6%) by both observers. Inter-observer variability was 0.703, but when omitting the usually undebatable 0+ cells, this variability showed to be 0.278.
HER2 scoring of CTC by two observers. HER2- (0+/1+)HER2+ (2+/3+)HER2- (0+/1+)2263 (83%)131 (4.8%)HER2+ (2+/3+)152 (5.6%)175 (6.4%)
24 of 65 patients had at least 80% 0+ CTCs (≥96% HER2- cells). Of these patients, 5 were HER2+ based on their PT. Oppositely, 10 and 20 patients harboured at least 40% and 10% HER2+ CTCs respectively. From these 20 patients only 10 were diagnosed with HER2+ disease on PT or Meta and 1 was shifted form HER2- PT to HER2+ Meta.
The digital scoring system was able to identify four groups with different HER2 expression levels. When comparing the identified clusters with the manually scored cells the two moderately related clusters showed to contain almost only 2+ and 3+ CTCs. A very isolated cluster contained almost solely 0+ CTCs.
Discussion:
The manual scoring system showed to be feasible, however we noticed that there are some discrepancies regarding the scoring of 1+ to 3+ cells. The digital scoring is able to predict the outcome and can by itself cluster CTCs into 4 groups. It strongly distinguishes between the HER2+ and HER2- cells. HER2+ status can change during disease progression, both with gain and loss of HER2 positivity. This can be monitored using CTCs.
Citation Format: Brouwer A, van de Wiel M, Peeters B, van Dam P-J, Vermeulen P, Peeters M, Van Laere S, Peeters D, Dirix L. Manual and digital detection of HER2 status of 2721 circulating tumour cells in patients with metastatic breast cancer. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P3-04-01.