Episode 13: Lymph nodes

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For over a century it’s been known that one of the first places that breast cancer (and most cancers) will travel is to nearby lymph nodes. For breast cancer, the first lymph nodes involved are usually the ones in the axilla.

Historically, patients with breast cancer not only had a mastectomy or lumpectomy to remove the tumor in the breast, but also surgery to remove as many lymph nodes in the axilla as possible. That surgery is called “axillary lymph node dissection.” It was thought that to be important because if you left any cancer-containing lymph nodes behind, the patient’s cancer would come back, and would often kill her.

The trouble is that lymph nodes are important. If you take them out, you disrupt the normal flow of lymphatic fluid from the arm back into the chest. (See episode 3 for more on this topic.) The arm can develop what’s called lymphedema: swelling that can be uncomfortable and sometimes permanent. The more lymph nodes removed from the armpit, the more likely the patient is to develop lymphedema.

Also, a good percentage of patients who underwent axillary lymph node dissection didn’t turn out to have any cancer in their lymph nodes. So those patients had the risks of that big surgery without any clear benefit.

So doctors thought, what if we could figure out which patients had cancer in their lymph nodes and only do the axillary lymph node dissection on them? How cool would that be??

There are a lot of lymph nodes in the axilla. It turns out that different areas of the breast drain to different lymph nodes.

If you could find the first few nodes that a breast tumor was draining to, you could just remove them and look at them under a microscope. If you didn’t see any cancer in those nodes, you could be pretty sure that none of the other lymph nodes in the patient’s axilla would have cancer, either. And if you only removed a few lymph nodes, the patient wouldn’t be at very high risk for developing lymphedema. Only if you did see cancer in those first few nodes would you go back and do the full axillary lymph node dissection.

The doctor injects a blue dye, a radioactive chemical, or both around the tumor. That dye or chemical is taken up by the breast's lymphatic channels. The doctor then looks in the armpit for lymph nodes that have turned blue and/or ones that are radioactive. (The doctor uses a Geiger counter-like device to find the radioactive ones.)

The first lymph nodes that a cancer spreads to are called the sentinel lymph nodes. The procedure of removing them is called a sentinel lymph node biopsy.

Sentinel lymph node biopsies are also used in melanoma and cancers of the mouth & throat area. We're investigating using the technique in other cancers, too.

Be aware, we doctors are still trying to figure out how important it is to surgically remove all involved lymph nodes. Expect our current understanding to change rapidly in the future as more research is done.