HER2 Testing Errors
Question: My pathology results showed my cancer was 3+ but FISH was done too and it showed a 1.7 so my doctor said I am not positive and therefore don’t qualify for Herceptin. From what I read 3+ is positive.
Answer: You are correct—a 3+ result by immunohistochemistry (IHC) is positive. If the laboratory that did your test is following the new rules for HER2 testing then there was no need to go to FISH. There is usually an outstanding correlation with 3+ by IHC and amplification by FISH so I am concerned maybe the lab over-called the IHC and you were really a 2+. Most cancers that are 2+ are not amplified by FISH which your cancer wasn’t with a ratio of 1.7. I would ask your doctor to check into why FISH was done and to see if the pathology lab that ran your IHC test really called it 3+ and maybe ask to have it repeated or performed at another laboratory.
Definitely, get a second opinion from another pathology lab. Scoring Her2 is difficult and subjective, and it isn’t unusual for two pathologists to disagree on the same case. This is important enough to get right; you want to take Herceptin if it can help you, but you don’t want to expose yourself to the side effects and expense if it can’t.
I completely agree. There are many studies, usually from large clinical trials, that show that local pathology labs and the central pathology review study labs disagree frequently on HER2 status. One of the most significant is the Breast Intergroup (N9831) study where the central review lab only agreed on 74% of HER2 IHCs and 66% of HER2 FISH!