The most common sign of cancer cells in the lymph nodes is that one or more of the lymph nodes becomes enlarged or feels hard. However, if there are only a small number of cells in the lymph nodes, they may feel quite normal, and it is only possible to tell that a cancer is present by removing part, or all, of the lymph node and examining the cells in a laboratory. However, it is important to remember that lymph nodes can be enlarged for other reasons, such as infections.
If the lymph glands are deep inside chest or abdomen, they may cause pressure on surrounding organs or structures. This can lead to symptoms like breathlesness or backache.

Sometimes a lymph node, or group of nodes, may appear larger than they should be on a scan, such as an ultrasound scan, CT scan or MRI scan. This may be a sign that there is a secondary cancer in the lymph nodes.

Cancerous tumours are made up of millions of cells. Some of these cells may break away from the primary cancer and travel in the bloodstream or the lymphatic system to another part of the body. They can stay dormant in such places for many years, or can grow into secondary tumours.

Cancer found in lymph nodes, in a part of the body far away from an original primary tumour, is usually recognised as being a secondary rather than a new primary cancer. Under a microscope, the cells will look like cells from the original type of cancer. For example, when a lung cancer has spread to the lymph nodes, the cells in the lymph nodes look like lung cancer cells.

In some people, when the original tumour is diagnosed, doctors will also remove some nearby lymph nodes. It is important to know whether or not a primary cancer has spread to any nearby lymph nodes, because it helps the doctors to estimate the risk of the cancer coming back, and to decide whether or not further treatment is necessary.

Cancer can develop in the lymph nodes in two ways. It can either start there as a primary cancer, or it can spread into the lymph nodes from a primary cancer elsewhere in the body. If cancer spreads into the lymph nodes from another part of the body, this is known as secondary or metastatic cancer. Cancer that starts in the lymph nodes themselves is called lymphoma.