While having surgery to remove part or all of the breast, many people also need to have a few or more underarm lymph nodes removed. Lymph from the breast tissue drains into these nodes — and it sometimes carries cancer cells along with it. If cancer cells are found in the nodes, there is greater risk that the cancer has traveled or could travel to other parts of the body. This plays an important role in making treatment decisions.
In the past, surgeons typically removed many or most of the underarm lymph nodes, a procedure called axillary lymph node dissection (ALND). But now, when possible, they favor a more limited procedure called sentinel lymph node biopsy (SLNB). This surgery removes just the first few lymph nodes — the “sentinel nodes” — that drain fluid away from the breast. The surgeon identifies the sentinel nodes by mapping the flow of lymph with a special radioactive substance or blue dye, then removes them and sends them to be examined under a microscope. If the sentinel nodes are free of cancer cells, then no additional nodes need to be removed.
If the sentinel nodes do contain cancer, more lymph nodes in the region may need to be removed — either as an additional part of the SLNB procedure or at a later date. The more extensive procedure is called axillary lymph node dissection (ALND). This decision is made on a case-by-case basis.
If the surgeon proceeds to ALND, then he or she will take out the next section of axillary tissue that contains lymph nodes. Once that tissue is examined under a microscope, your surgeon can tell you how many lymph nodes were removed. Depending on whether you have SLNB or the more involved ALND, you could have anywhere from two or three to up to 40 lymph nodes removed from under your arm. The surgery itself also can damage some lymph vessels.
So think about it: All of the lymph fluid from that side of the upper body — the chest and back from the bottom to the top of the ribcage, as well as the arm and hand — has been accustomed to draining to the axillary lymph nodes. The more lymph nodes and vessels removed, the greater the likelihood that this flow is going to be disrupted. The lymph has to find alternate pathways through which to move.
Radiation treatments also can affect the lymphatic system. Radiation therapy can cause the formation of scar tissue that presses on or narrows the remaining lymph vessels and nodes. This interferes even further with the flow of lymph out of the arm and upper body. Radiation directly to the underarm carries the most risk for radiation-related lymphedema, since this is where most of the nodes are, but radiation to the breast or chest areas also increases risk.