[AlaskaAngel]

As Hopeful pointed out, these tests are "equal" if done correctly. However, because not all labs do as good of a job on them, the result is:

If they are done in a place such as a major cancer center where they are done in greater volume, the people doing the test are more likely to have more practice at doing them and have better access to better training and repeat evaluation in doing them correctly than when they are done now and then in a smaller lab, say, in a more rural area.

That results in a decision in one place by an onc that the volume is high enough to believe that the IHC is accurate enough, and a decision in another place by an onc that the testing probably needs to be confirmed by FISH testing. One might ask logically then why the IHC was done at all in the first place. In smaller facilities, cost is more of a factor, and although I am only guessing, the cost is probably less for IHC testing. Since only 1/3 of bc patients are HER2 (and many are only marginally so), doing the IHC first would be more economical and practical.

Hope that helps.

A.A.

P.S. Which may also mean that it is possible that HER2's can be "missed" in areas that use the IHC but don't have high volume testing.