RNA-Seq of Circulating Tumor Cells in Stage II-III Breast Cancer

BACKGROUND: We characterized the whole transcriptome of circulating tumor cells (CTCs) in Stage II-III breast cancer to evaluate correlations with primary tumor biology. METHODS: CTCs were isolated from peripheral blood (PB) via immunomagnetic enrichment followed by fluorescence-activated cell sorting (IE-FACS). CTCs, PB and fresh tumors were profiled with RNA Seq. Formalin-fixed, paraffin-embedded (FFPE) tumors were subjected to RNA Seq and NanoString PAM50 assays with Risk of Recurrence (ROR) scores. RESULTS: CTCs were detected in 29/33 (88%) of patients. We selected 21 cases to attempt RNA Seq (median number of CTCs=9). 16 CTC samples yielded results that passed quality control metrics. These samples had a median of 4,311,255 uniquely mapped reads, less than PB or tumors. Intrinsic subtype predicted by comparing estrogen receptor (ER), progesterone receptor (PR) and HER2 versus PAM50 for FFPE tumors was 85% concordant. However, CTC RNA Seq subtype assessed by the PAM50 classification genes was highly discordant both with the subtype predicted by ER/PR/HER2 as well as by tumor PAM50. Two patients died of metastatic disease - both had high ROR scores and high CTC counts. We identified significant genes, canonical pathways, upstream regulators and molecular interaction networks comparing CTCs by various clinical factors. We identified a 75-gene signature with highest expression in CTCs and tumors taken together that was prognostic in The Cancer Genome Atlas and METABRIC datasets. CONCLUSION: It is feasible to use RNA Seq of CTCs in non-metastatic patients to discover novel tumor biology characteristics. 6 peripheral blood samples from healthy individuals (negative controls) were compared to circulating tumor cells from n=16 patients, with comparison to the primary tumors available for n=12 of these patients