Is the HER-2 gene only found in breast tissue?

I seem to recall reading something that said it was a gene found in all cells and its purpose dealt with cell division and replication. But I can't remember where I read it to go back and check. If this is so, wouldn't it be a factor in other cancers? I'm confused about this and hope someone who knows more about the ins and outs of it will respond.

I tried asking my oncologist but my appt. with him was cancelled (that's another story) and the nurse who infused me (Herceptin) forgot to ask him. (He recently merged his practice with another and I'm in the process of looking for another oncologist. Love him but the new practice is another story!)