Sentinel Lymph Nodes

Sen.ti.nel: A soldier or guard whose job is to stand and keep watch.

I have a close friend who was standing in the shower one day and noticed a lump under her arm. She is in medicine, and despite trying to blow it off she knew what it might herald, and eventually manned (I mean womanned!) up and made herself an appointment with a breast surgeon. Ten years ago she was diagnosed with metastatic breast cancer. She had a mastectomy with lymph node dissection. She had treatment. She got off her meds, had a child at 47. She has a handsome first grader. She is in her early 50's and she looks like a movie star in her late 30's.

I look at a lot of sentinel lymph nodes. Sure, there are other ones besides those in the breast axilla, but they are by far the most routine. The surgeon injects a radioactive tracer attached to blue dye around the tumor and follows the  path to the nodes that the tumor cells would take to locate them. There are a bunch of nodes in the axilla, but chances are if the cancer is not in the sentinel nodes - the guards - then it won't have traveled any farther. There are exceptions to the rule but like most rules the exceptions they are few and far between.

In the gross room we receive the sentinel nodes and our techs do a gross analysis. Lymph nodes are floppy and brown-grey, much the size and consistency of a kidney bean. Massive metastases are grossly obvious - stellate, white hard infiltrates scream positivity, which is easily confirmed by microscopic examination. But many metastases are insidious - not grossly obvious. We do step examination of multiple levels of sentinel lymph nodes (sometimes there are more than one) which can fill a tray or two of slides (20 slides per tray).

When I get a tray or two of sentinel lymph nodes I often wait until I have a cup of coffee to settle down and look at them - it takes time and major focus. The kidney bean shaped node is full of small round blue cells called lymphocytes with reactive germinal center follicles - white round circles dotting the blue landscape. The border contains the sinus of the node - the most likely place (a small space) for occult isolated tumor cells or clusters of cancer to sneak into. If you blink you might miss some. It takes slow and methodical cruising at high power. I occasionally sub at breast conference for my partner who presents at it regularly, and I am continually amazed at the tiny, almost invisible foci my partners unfold. I know how hard it is to really see that. I have great respect for the amount of time and effort it demands to discover it. I know, I do it too, it's part of the job, but it continually amazes me.

These days we routinely use pancytokeratin immunostains to look for small, isolated tumor cells and clusters. While this is a nice adjunct to help us sleep better at night, it is not a safeguard or panacea to allow us to slack on the job of the routine H&E slide. I have seen cancer cells on H&E that are cut away on the special stains. I have seen cancer cells on the special stains that are not on the H&E (this stands for hematoxylin and eosin - the pink and blue Easter egg colors that we use to stain all tissue for examination). It's enough to keep you up on a bad night, wondering what you might have missed.

You would never guess my friend had metastatic breast cancer - I didn't even know for the first few years I knew her - she was diagnosed before I met her. She has shared struggles with treatment side effects but doesn't touch on what I know I would obsess over - fears of leaving behind my children. She is a perfect picture of poise, elegance, and grace. But she has this underlying Tiger Mom thing, an aggressiveness and intensity that I know must have come with what she has faced in life and dealing with the unknown of the future. Sure, we all have unknowns - I could die in a car crash tomorrow but I haven't dealt with nearly as much adversity as she has in my own personal health arena (yet!).

I love the definition of sentinel. The guard. The lymph node that tries to hold it all in check. I can empathize, as I am sure my friend does too. We women in medicine, and mothers too - we are always on constant watch and hyper-vigilance. For our patient's health, and for that of our children. We can't protect our charges from everything, but that doesn't keep us from trying with all of our power and might. It's the best we can do, and it's good enough.