Spatiotemporal Quantification of Metastatic Tumour Cell Growth and Distribution in Lymph Nodes by Whole-Mount Tissue 3D Imaging

Lymph nodes (LNs) are a common site of metastasis in many solid cancers. Tumour cells can migrate to LNs for further metastatic colonization of distant organs, indicating poor prognosis and requiring different clinical interventions. The current histopathological diagnostic methods used for the detection of clinical lymph node metastasis (LNM) still have some limitations, such as incomplete observation. To obtain a complete picture of tumour-metastasized LNs at spatial and temporal scales, we used 3D imaging of solvent-cleared organs (uDISCO) and 3D rapid immunostaining. MC38 cells tagged with EGFP were injected into the left footpad of C57BL/6 mice. Draining lymph nodes (DLNs) obtained from these mice were cleared using uDISCO. Metastatic colorectal cancer (CRC) cells in various regions of DLNs from mice at different time points were quantified using whole-mount tissue 3D imaging. The results revealed several stages of tumour cell growth and distribution in LNs: 1) invasion of lymphatic vessels (LVs) and blood vessels (BVs); 2) dispersion outside LVs and BVs for proliferation and expansion; and 3) re-entry into BVs and efferent lymphatic vessels (ELVs) for further distant metastasis. Moreover, these data demonstrated that mouse fibroblast cells (MFCs) could not only promote the LNM of tumour cells but could also metastasize to LNs together with tumour cells, thus providing a “soil” for tumour cell colonization. In conclusion, whole-mount tissue 3D imaging and spatiotemporal analysis of LNM may together constitute an auxiliary method to improve the accuracy of clinical LNM detection in the future.