Whole Genome Sequencing in single CTC improves clinical outcome in Her-2 negative breast cancer patients

Abstract

Background Tumor tissues are usually highly heterogeneous and difficult to characterize which could mislead treatment strategy. Circulating tumor cells (CTCs) represent the most active and invasive tumor cells. This study explored the feasibility of individualized treatment of breast cancer patients based on genome sequencing of single cell CTC. Methods Twenty-four CTCs were identified in three patients with breast cancer. For each patient, one polyploid CTC was captured and on which the whole genome sequencing (WGS) was performed. Based on the histopathological Her-2 status in tumor tissue and the HER2 gene status in WGS results of CTC, we adjusted treatment strategies, and monitored disease progression. Results Patient ID1 and ID2 are Her-2 positive in both primary tumor and HER2 abnormal in the DNA of CTC. In patient ID3, histological examination of primary tumor and liver metastases revealed Her-2 negative, but the WGS analysis of CTC showed that the HER2 gene was amplified and mutated. After adjusting treatment according to the results of CTC sequencing, the liver metastases and pleural effusion were significantly reduced, CTC number and ctDNA burden were decreased. In addition, some potential therapeutic targets and mutations in drug-resistant genes were found. Conclusion The results of CTC sequencing effectively guided treatment of a patient with HER2 gene amplification/mutation in CTC but with Her-2 negative on tumor tissue. CTC sequencing is useful in resolving the heterogeneity of tumors and providing precision medicine for patients.