The number of lymph glands (lymph nodes) under the arm varies from person to person. Estimates are that the numbers can be anywhere between 20 to 50 glands. These glands are normally very small and embedded in the fatty tissues, so they are often very difficult to see with the naked eye.
If lymph nodes are involved with cancer then they may become swollen and enlarged and are more obvious to see.
When a surgeon explores the area under the armpit (called the axilla) during an operation to remove a breast cancer he/she has two main aims. The one is to remove any cancerous lymph nodes and the other is to detect if there are any minute traces of cancer cells in the lymph nodes which is important in deciding whether or not you should have further treatment such as hormone therapy or chemotherapy (adjuvant treatment).
As the normal lymph glands are often very hard to see it is not easy for the surgeon to be certain how many glands they have removed. There are a number of current approaches to removing the lymph glands. The current guidelines suggest that at least four glands are needed to make a reliable assessment of whether or not the breast cancer has spread to any of the glands. So usually the surgeon will try and take away enough tissue from the axilla to ensure there will be at least four glands available for examination under the microscope.
Some surgeons believe that it is important to try and remove all the glands to make sure none are missed and so do an operation called an axillary clearance. This has the advantage of giving greater certainty that there is no cancer in the lymph glands but there is also a increased risk of side effects such as swelling of the arm.
Another approach that is now being tried is to inject some dye or radioactive material into the tissue near the tumour and it is then possible during the operation to see the glands in the axilla into which the dye or radioactive has travelled to (these are called sentinel lymph nodes). These one or two glands are the ones that are most likely to contain cancer cells and are removed and examined under the microscopic for cancer cells. If they are clear it is very unlikely that any of the other glands will be affected. If they do contain cancer cells than the rest of the glands are usually removed for examination under the microscope. This approach is still being tested to make sure it is as good as the current methods and is not yet routine practice in the UK.