Before or during surgery to remove an invasive breast cancer, your doctor removes one or some of the underarm lymph nodes so they can be examined under a microscope for cancer cells. The presence of cancer cells is known as lymph node involvement.
Lymph nodes are small, bean-shaped organs that act as filters along the lymph fluid channels. As lymph fluid leaves the breast and eventually goes back into the bloodstream, the lymph nodes try to catch and trap cancer cells before they reach other parts of the body. Having cancer cells in the lymph nodes under your arm suggests an increased risk of the cancer spreading.
When lymph nodes are free, or clear, of cancer, the test results are negative. If lymph nodes have some cancer cells in them, they are called positive. Your pathology report will tell you how many lymph nodes were removed, and of those, how many tested positive for the presence of cancer cells. For example, 0/3 means 3 nodes were removed and 0 were positive, while 2/5 means 5 were removed and 2 were positive.
Your results will also tell you how much cancer is in each node — ranging from a few tiny cells to many cells that can be seen easily. You might see this reported as:
- Microscopic (or minimal): Only a few cancer cells are in the node. A microscope is needed to find them.
- Gross (also called significant or macroscopic): There is a lot of cancer in the node. You can see or feel the cancer without a microscope.
- Extracapsular extension: Cancer has spread outside the wall of the node.
The more lymph nodes that contain cancer cells, the more serious the cancer might be. So doctors use the number of involved lymph nodes to help make treatment decisions.