The lymphatic system is vital for our immunity. It consists of a fluid called lymph, which is processed in several organs and circulated via thin lymphatic vessels. Lymph nodes are small bean-shaped and pea-sized structures present at intervals along these lymphatic vessels. There are about 500 to 800 lymph nodes across the body. Some areas like the neck, armpit, and groin have a higher density of nodes.
Cancer cells from an organ can spread to the lymph nodes around it, often in a predictable path and pattern. This is called “regional spread.” A cancer that has spread to regional nodes (nodes close to the primary cancer) can often still be cured. Sometimes nodes far away from the primary cancer (“distant spread”) are involved – this may indicate incurability. Some cancers arise in the lymphatic system itself (called lymphomas). Lymphomas can also manifest with enlarged lymph nodes – but they are evaluated and treated differently and not the topic of this post.
Cancer involvement of the lymph nodes can sometimes be picked up by pre-operative tests. But often, the cancer cells are too small to be seen on even the most sophisticated scans available.
Surgery for cancer often includes the removal of lymph nodes because:
- Nodes that are obviously affected have to be removed (part of treatment)
- Nodes that may be involved have to be sampled (part of staging). These sampled nodes are analyzed by the pathologist under the microscope to see whether they contain any cancer or not.
In the second instance, the need to remove nodes, therefore, depends on the likelihood of the nodes being involved with cancer. This in turn depends on
- The organ affected by cancer (for example stomach cancers commonly spread to the nodes, whereas brain cancers rarely do)
- The type of cancer (for example melanoma of the skin is more likely to have lymph node metastases, whereas basal cell cancer of the skin rarely involves nodes)
- The clinical (pre-operative) stage of cancer (the higher the stage of the primary tumor, the more the chances of lymph node spread)
The cancer’s location, type, and stage determine which lymph nodes need to be removed during surgery.
Recent advances in oncological surgery have enabled accurate staging with minimal nodal dissection (“the sentinel node concept”). At the other end of the spectrum, extended lymph node dissections are also helping select patients with cancer achieve a cure not possible earlier.