origional dx er,pr+/mets er,pr,- and her2+

My origional dx 13 years ago was stage 1 er, pr + and the mets I was dx with 5 months ago is er, pr, - and Her2+. I had a biopsy of a 4cm cyst removed from the other breast that was benign and there are no other sypmtom of a new primary. Is it possible for the tumor to change it's hormone status? Has this happened to anyone else? If Her2 is so aggressive, why did it take 13 years for me to have physical symtoms.(I have a compression fracture in my spine) The last CEA test I had was January 1998, which was normal. I had kidney stones November 2001 which can be a symptom of bone mets, which I have.