[CPA]

Erin,

Maybe this will help (and if I am wrong, I am sure that somebody will correct what I am posting).

As I understand, FISH measures the number of a specific gene on a certain chromosome. If you have too many (more than 2) then you are positive. It does not matter if you have 4, 5 or 12... Anything over the normal is too many.

The IHC test is essentially a stain done on specially prepared slides of b/c cells. The darker the stain, the more receptors present. If the slide is "clear" or lightly stained, you are a 0 or 1, while darker slides are 2 or 3. Becasue there is some interpretation involved in matching the color to the score, there is some room for error in this test, especially between 1 (negative) and 2 (positive).

So, the FISH actually checks for the genetic abnormality, while the IHC checks for the results of the genetic abnormality (too many receptors).