Abstract PS2-11: Ctc-her2+ a novel subset in stage IVaggressive: Molecular correlations, outcome and clinical characteristics in metastatic breast cancer

Abstract

Abstract Background The enumeration of Circulating Tumor Cells (CTCs) in the peripheral blood of patients (pts) with metastatic breast cancer (MBC) showed prognostic value independent of clinic-pathological characteristics and proposed as a new tool for Stage IV stratification. Molecular characterization of CTCs with analysis of standard HER2 and estrogen-receptor (ER) status provides additional predictive value. The presence of HER2 positive CTCs (CTCs-HER2+) has been documented in pts with HER2 negative MBC and suggestive of tumor heterogeneity. The molecular features associated with the detection of these cells and the clinical significance of CTCs-HER2+ remains of unclear clinical significance. The lack of validated prospective trials limits the use of this immunophenotypic characterization as a prognostic and predictive factor. We conducted an analysis of a large cohort of patients with MBC evaluated for CTCs enumeration (CTCs+), molecular analysis of CTCs (CTCs-HER2+) and ctDNA. Methods The IRB-approved study prospectively analyzed blood samples of pts with MBC enrolled before starting a new line of therapy. Samples were collected from pts treated at Northwestern University (Chicago, IL) between 2016 and 2020. ctDNA was analyzed using the Guardant360 NGS assay (Guardant Health) with a specific focus on the detection of ERBB2 mutations. CTCs were enumerated through CellSearch™ (Menarini Silicon Biosystems, Bologna, Italy), and characterized for HER2 expression using the CellSearch CXC Kit. HER2+ CTCs were divided in 4 different categories (0,1+,2+,3+), leaning on fluorescence intensity, as previously reported by Riethdorf et al. Pts with <5 CTCs (stage IV indolent ) were excluded from the analysis. The cHER2 ratio, defined as the sum of 2+ CTCs and 3+ CTCs divided by the total number of HER2+ CTCs was used to split the remaining pts in 2 different subgroups: cHER2 ratio> 0.75 (cHER2high), cHER2 ratio<0.75 (cHER2low). Pts' characteristics and genomic alterations were compared between these two subgroups and a long-rank test was performed to analyze the outcome (progression-free survival, PFS). Results A total of 247 pts with MBC about to start new therapy were enrolled. 136 patients (55%) demonstrated CTCs count ≥ 5 (stage IV aggressive). Of these, 111 pts had a blood sample bearing HER2+ CTCs. 88 pts were classified as cHER2low, while 32 were allocated in the second subgroup (cHER2high). The clinic subtype distribution of the two groups was as follows: 65% ER+, 19% HER2+ and 16% TNBC among cHER2low, compared to 55% ER+, 38% HER2+ and 7% TNBC among cHER2high pts. The HER2+ subtype was significantly more represented in the cHER2high group (p<0.05), along with ERBB2 mutations (p<0.05). We observed a total of 89 events (progression to treatment), 67 and 22 respectively. The median PFS was 87 days in the cHER2low and 209 days among cHER2high pts (log Rank test, p<0.001). Conclusion This study shows a significant association between the cHER2 ratio and outcome in pts with Stage IV aggressive disease, suggesting a potential predictive/prognostic role of this biomarker among MBC pts bearing CTC-HER2+. cHER2high pts, in which blood was collected a prevalent number of CTC-HER2+ 2+ and 3+, were more likely to have a HER2 FISH amplification by tissue biopsy and ERBB2 gene alteration by ctDNA. These findings, taken together, suggest a potential role of these subsets of CTC-HER2+ in the characterization of the HER2+ metastatic disease. The cHER2low is intrinsically characterized by a higher percentage of CTC-HER2+ 1+. This CTC-HER2+ subset of cells is commonly detected among all subtypes but, more frequently in ER+ disease and their significance remains unclear. Exploring the underlying biological nature of the CTC-HER2+ 1+ could allow to better understand the role these cells in the natural evolution of the MBC. Citation Format: Paolo D'Amico, Qiang Zhang, Lorenzo Gerratana, Youbin Zhang, Ami Shah, Carolina Reduzzi, Andrew Davis, Saya Jacob, Firas Wehbe, Amir Behdad, Giuseppe Curigliano, Massimo Cristofanilli. Ctc-her2+ a novel subset in stage IVaggressive: Molecular correlations, outcome and clinical characteristics in metastatic breast cancer [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS2-11.