Is Her2 only in BC?

I met a lady today through a friend who has recently been diagnosed with stage 1V ovarian cancer. I asked about the Her2 factor and she asked her doctor who said it was specfic to BC because of the hormonal properties. Then, she said it was confusing to her at this point. My question. Is Her2 only for BC and no other cancers? I thought it did apply to ovarian where that is hormonal. It seems we never run out of questions to ask on this board. Hugs, Sandy