So, McCain got the melanomas and nearby lymph nodes removed, and the doctors hope that will cure his recurrence of cancer. I got to thinking about lymph nodes. I have a rudimentary (and probably wrong) idea of what lymph nodes do, but could someone;
Give a full description of lymph nodes and their function;
Explain how they can be removed willy nilly without appreciable problems in cancer patients (I mean, they are usually removed before anyone knows if the cancer has spread to them, and then biopsied;
Tell if there is a critical point at which you can’t remove any more lymph nodes without causing serious problems.
Lymph nodes are little capsules of mostly immune cells. They’re job is to filter lymph, kind of like the way an oil filter works. The lymph enters the node from the outside, and it basically filters through the node (and all of the immune cells) before exiting from a lymph vessel originating in the center of the lymph node.
Now, what is lymph - the blood brings oxygen and nutrients by way of arteries to the capillaries. The capillaries are basically leaky in most places, and so the blood pressure forces some fluid out of the capillaries. This fluid consists of water, protein, and other things (nearly blood without the cells) and is what is called lymph. This makes its way by small lymph vessels to the node, and then from the node in larger lymph vessels back into the venous circulation. This is oversimplified, but basically correct.
With cancer, the tumor is thought to “shed” cells at the beginning of spreading (metastasis), and these go, like almost everything else (bacteria in infection, foreign bodies, etc.) to the lymph nodes.
The lymph vessels form a characteristic drainage pattern. For every patch of skin, there is a defined lymphatic pattern, with the primary nodes that the lymph drains into. The lymph nodes are fairly variable in location, but there are some conserved patterns. So, in cancer, depending on where the cancer is, you can predict which lymph nodes will be the first to receive the metastases. The first line of lymph node, and specifically the closest draining lymph node is called the “sentinel node.” In order to find them, you have to do a dissection – you make quite a wide exploration of the tissue near where the nodes are supposed to be.
So, if you have cancer, let’s say on your scalp, the cutaneous lymph drainage I believe goes to lymph nodes behind your head and in your neck (I think, anatomy was 3 years ago). For breast cancer, the primary lymph nodes are in the armpit (axilla in anatomical terms). This is why they never do a mastectomy or lumpectomy alone – it is always coupled with an axillary node dissection.
In surgery, they dump the nodes into liquid nitrogen and send them to pathology. The pathologist slices and stains them (a frozen section) and examines them microscopically to find any suspected cancer cells. This is a preliminary exam, but can tell the surgeon if continued dissection is necessary (the first line of nodes is cancer positive) or if it is probably OK to sew the guy back up.
Usually, after extensive node dissection, people do have problems with lymphatic drainage in the area served by the dissected nodes. For a woman who has had left axillary dissection, she is forbidden to do heavy work with the arm (to lessen injury and infection risk), and can’t have blood taken from the arm. Often times, after extensive node dissection, one can develop lymphedema, or swelling associated with improper lymphatic drainage.
Also, if the nodes are all grossly positive, or other evidence of extensive metastasis is found during surgery, the surgeon may opt to quit dissecting and trying to remove cancer, as a surgical cure may be impossible.
The real problem with metastasis is not gross spread, but rather the metastasis of only 1 or 2 cells. This can easily be missed, and one can undergo a surgical “cure” only to have a relapse in the area or a near area 3 or 4 years later. This is called “micrometastasis” and it is why purely surgical cures for cancer are becoming rarer – it is now common for many types of cancer to give chemo or local radiation for prevention of micrometastasis as well as surgery.