You remember the lymph node system that I described in Chapter 2? How can we check whether or not the cancer has spread through this system?
Normal lymph channels are like cotton threads. Normal lymph nodes (glands) are soft, smaller than a pea and cannot be felt through the skin. If cancer gets into the lymphatic system it usually grows in the lymph nodes, making them bigger and harder. This is usually painless.
Much less often, lymph spread takes a different form—the cancer can actually grow in the lymph channels. If the affected channels are in the skin, the appearance is usually that of a raised, red ‘rash’. One of the most troublesome sites for this type of spread is in the lungs. The solid cores of cancer cells running through the lymphatic vessels make the lungs very stiff. This causes cough and shortness of breath. Unfortunately this problem can be hard to diagnose, because it is often difficult to see on an X-ray in the early stages.
If the cancer fills the nodes or blocks the lymph channels, it prevents that part of the lymph system from carrying out its usual job. One of these is to drain excess fluid from the tissues. So, for example, if the affected nodes are in the armpit, the arm may swell up.