Shallow WGS of individual CTCs identifies actionable targets for informing treatment decisions in metastatic breast cancer

Background We report copy-number profiling by low-pass WGS (LP-WGS) in individual circulating tumour cells (CTCs) for guiding treatment in patients with metastatic breast cancer (MBC), comparing CTC results with mutations detected in circulating tumour DNA (ctDNA) in the same blood samples.Methods Across 10 patients with MBC who were progressing at the time of blood sampling and that had >20 CTCs detected by CellSearch^®, 63 single cells (50 CTCs and 13 WBCs) and 16 cell pools (8 CTC pools and 8 WBC pools) were recovered from peripheral blood by CellSearch^®/DEPArray™ and sequenced with Ampli1 LowPass technology (Menarini Silicon Biosystems). Copy-number aberrations were identified using the MSBiosuite software platform, and results were compared with mutations detected in matched plasma cfDNA analysed by targeted next-generation sequencing using the Oncomine™ Breast cfDNA Assay (Thermo Fisher).Results LP-WGS data demonstrated copy-number gains/losses in individual CTCs in regions including FGFR1, JAK2 and CDK6 in five patients, ERBB2 amplification in two HER2-negative patients and BRCA loss in two patients. Seven of eight matched plasmas also had mutations in ctDNA in PIK3CA, TP53, ESR1 and KRAS genes with mutant allele frequencies (MAF) ranging from 0.05 to 33.11%. Combining results from paired CTCs and ctDNA, clinically actionable targets were identified in all ten patients.Conclusion This combined analysis of CTCs and ctDNA may offer a new approach for monitoring of disease progression and to direct therapy in patients with advanced MBC, at a time when they are coming towards the end of other treatment options.Subject terms: Prognostic markers, Breast cancer