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How can cancer cells spread to lymph nodes through the lymphatic system?

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Diagram of the human lymphatic system highlighting lymphatic vessels and major lymphoid organs, including lymph nodes, adenoids, tonsils, thymus gland, spleen, appendix, bone marrow, and ducts. — lymphatic system The human lymphatic system, showing the lymphatic vessels and lymphoid organs.

Cancer cells spread to lymph nodes through a process of metastasis, which involves several complex steps. To reach the lymphatic system, tumor cells must first detach from neighboring cells and break through supporting membranes within the primary tumor site.1

To gain access to lymphatic channels, these cells use enzymes to digest and break down the extracellular matrix, creating a path through surrounding tissues. Once they penetrate the basement membrane of a lymphatic vessel, the cancer cells enter the lymph circulation.12

The lymphatic system naturally acts as a filter for the body, and as cancerous cells travel through these vessels, they can become trapped and concentrated within lymph nodes. Once trapped, the cells may proliferate, forming secondary tumors. This spread often begins in a "sentinel" lymph node—the first node reached by the cancer cells—before potentially moving to others. Because this process complicates treatment, it is a critical factor in assessing the stage and management of many cancers.23