Complementary information provided by simultaneous sequencing of CTC, cfDNA and metastatic tissue in endocrine-resistant metastatic breast cancer

Background: Endocrine resistance is a major cause of therapeutic failure in metastatic breast cancer (MBC). The information provided by DNA sequencing of plasma cell free DNA (cfDNA) and by the analysis of circulating tumor cells (CTC) may be useful to determine the occurrence and type of endocrine resistance. However, different levels of concordance between cfDNA and CTC, and also between liquid biopsy and tissue biopsy, have been reported. Thus, the best strategy for performing DNA sequencing in the setting of therapeutic decisions for luminal MBC patients is not well defined. The purpose of this study was to determine the concordance between DNA sequencing data from CTC, cfDNA, metastasis, and primary tumor in endocrine-resistant luminal MBC.Methods: Using the same panel (10 genes) we performed simultaneous sequencing of cfDNA, CTC, metastases and primary tumor in 38 patients with luminal MBC. CTC isolation was performed with an Epcam-based immunomagnetic system. Concordance of DNA sequencing data of the different types of sample was analyzed and correlated with clinical data. Results: CTC were detected in 21% of the patients. The rate of detection of genetic alterations was 87.5% for CTC, 61.5% for cfDNA, 63.2% for metastasis and 67.7% for primary tumor, and involved mainly TP53, PIK3CA, ESR1 and AKT1. A higher number of mutations was found in cfDNA of MBC patients with progressive disease (p=0.02) and the same trend was observed for endocrine resistance (p=0.08), especially for PIK3CA, ESR1 and AKT1 mutations. Global concordance was low to intermediate between CTC and cfDNA, but significantly higher between CTC and metastasis. Concordance also varied according to the specific genetic alteration, with no ESR1 mutations detected in CTC and with a low concordance for PIK3CA and AKT1 mutations between CTC and cfDNA samples.Conclusions: DNA sequencing of different types of tumor samples (cfDNA, CTC, metastasis and primary tumor) may provide different rates of genomic alterations detection in luminal endocrine-resistant MBC. A moderate to low concordance, with discordances depending both on the clinical situation and on the sequenced gene, support the complementarity of the different samples, with cfDNA and metastatic tissue as the preferred sources of tumor DNA.