Lymphatic system is the mainstream for breast cancer dissemination and metastasis revealed by single-cell lineage tracing.

Cancer metastasis is the primary cause of cancer-related death, yet the forces that drive cancer cells through various steps and different routes to distinct target organs/tissues remain elusive. In this study, we applied a barcoding system based single-cell lineage tracing approach to study the metastasis rate and route of breast cancer cells and their interactions with the tumor microenvironment (TME) during metastasis. The results indicate that only a small fraction of cells, accounting for fewer than 3% of total barcodes, can intravasate from the primary site into the blood circulation, whereas more cells disseminate through the lymphatic system to different organs. Tumor cells derived from the same progenitor cell exhibit different gene expression patterns in different soils, and the cancer cell-TME communication paradigm varies significantly between primary and metastatic tumors. Furthermore, metastable cells require a prewired particular cytokine expression ability which may be specific for lymph metastasis route although the underlying mechanism requires further investigation. In summary, leveraging a single-cell lineage tracing system, we demonstrate that the crosstalk between tumor cells and the TME is the driving force controlling the preferential metastatic fate of cancer cells through the lymphatic system.