DEFINING MICROMETASTATIC DISEASE

The false-negative rate of conventional axillary dissection is about 15 percent,even in the hands of really good breast pathologists like Peter Rosen.The false-negative rate with sentinel lymph node mapping is likely to be in the range of five percent. In our own experience and in other centers, we are finding more metastatic disease per tumor size in this era than in the past. So, not only would I argue that sentinel node mapping is less surgery, but it’s actually finding more N1 disease that the medical oncologist can appropriately treat.Where this becomes problematic is that as we see lesser and lesser volumes of either cancer cells or extrinsic cells in the sentinel lymph node, where do we draw the line? The conventional division of two millimeters or less being micrometastatic disease is really artificial in the era of sentinel lymph node biopsy.

The nation is divided right now concerning the relevance of IHC- positive disease and axillary nodes. At one end of the spectrum are clinicians who say, “We don’t know what this means, so we shouldn’t do the test. ” There’s also an American College of Surgeons ’trial where the clinician and the patient are being blinded to IHC- positive disease. At the other end of the spectrum — which is where we are — clinicians are using this information on a case--by-case basis to treat patients. In the main, the overwhelming evidence is that micrometastatic disease really is clinically relevant. But, as we saw with tumor size in the breast, there’s a range. One cell in the lymph node cannot possibly have the same clinical ramifications as a cluster of cells or a millimeter of cells. So, fine-tuning that is where the research is currently aimed.

—Patrick Borgen, MD

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