Dear Chandi,

On the thought that the "devil is often times in the details," you might want to check and see what test is being performed on your sample. IHC testing measures the "overexpression" of HER-2 protein. This protein is relatively unstable, and, in part, is the reason why IHC testing is sometimes unreliable (along with lab error).

In contrast, FISH testing measures the overexpression of HER-2 genes. Genes, at a DNA level, are incredibly stable for long periods of time. I read one "retro" study that sampled tumors which were 18 years old. I note that Kathy's post indicates that her sample was retested after 19 years! Hopefully, if a FISH test is used, and assuming your sample was stored properly, you can be accurately retested.

I provided a cross-link below to a brief description of the PathVysion™ FISH-based DNA test. PathVysion™ is the FISH-based test mentioned on the Herceptin drug label. It may shed some light on this topic.