Pathology of NETs

Finding out the pathology seems like more detail than you want to process when you've gotten a diagnosis of cancer, but it is probably the most important piece of information as far as understanding the nature of the disease.  It's critically important that you understand what it means and what the various words are.  Unfortunately, many physicians may not be familiar with the details of the pathology.  I'll describe some of the key words and give you a sense of what they mean and what are the important features of the report.

So when you get a pathology report, it's important to know WHAT they are looking at.  In general, there are three types of tissue samples: fine needle aspiration, core biopsy, and surgical removal of the tumor.  

A fine needle aspiration means they put in a tiny needle into the tumor, sucked out some cells, and hope that's enough to tell what the tumor is.  It's pretty much only suited for identifying the type of tumor, but that's important if they can tell it is NET.  

A core biopsy is when they put in a big needle and cut out a core of tumor.  It too can tell you the tumor type, but with greater confidence.  Also, they may give a "sense" of how aggressive it is.  

Obviously, the most information comes from the surgical removal of the tumor where they can look at the whole thing, tell you how big it is, identify it with confidence, and tell if there are associated lymph nodes, etc.  The best way for them to identify it as neuroendocrine is by staining it with special antibodies; for NETs, the positive stains are generally synaptophysin and Chromogranin A.

Another important aspect of the pathology report is determining how fast the tumor grows.  Easiest way is called a "MITOTIC COUNT".  The pathologist looks under the microscope and counts the number of cells that are physically splitting.  If the tumor is aggressively growing, many cells are splitting.  If not, then few will be.  Another way of looking at this is the "Ki67" stain.  The pathologist can stain the slide for this protein and when it is highly active, it means the tumor is more aggressive.  We usually use these cutoffs for Ki67: 0-2% (low grade), 2-20% (mid grade), > 20% (high grade).

I hope that gives you a sense of how important it is to review the pathology.  There's a lot of complicated language in there which is why I always want you to see a specialist who is familiar with the information.  In fact, you may even consider a second opinion on the pathology review if there is no Ki67 stain.  

Eric Liu, M. D.