How can pathology of tumor change?

[sweetnvmbr00]

I am a 37 year old female.I had a prophylactic bi-lateral mastectomy in November 2007 after my identical twin sister was diagnosed with stage III invasive lobular carcinoma and we both tested positive for the BRCA1 mutation. In October 2008 while having final reconstrutive surgery the doctor removed a 5cm node in the upper axillary near peck and shoulder that came back positive for cancer. Since I have no breast tissue I was diagnosed metastatic tumor of unknown origin.
I received 4 AC and 4 Taxotere treatments and 28 radiation treatments to left reconstructed breast, axilla and coloar bone. After I was done with active treatment my oncologist said I was triple negative and therefor there was nothing else medically we could do. My receptor status was ER+(1%) PR-HER2-. I went to MD Anderson to get a second opinion and now I am being told that my pathology has changed an the tumor was ER+(70%) PR- HER2- by FISH. They want me to start Arimidex since I have no Ovary's. I don't understand how the pathology can change that much. I am waiting to hear back from the PA at MDA so she can sit down and go over the full report with me. Meanwhile I have picked up the script for the Arimidex but I am hesitating starting it until I speak with her. I have read Arimidex doesn't respond well if the tumor was PR-? Any thought on all of this would be greatly appreciated.
sweetnvmbr00

[japdip]

I don't think the Pathology of the tumor changed but when examined by different methods you can come up with different results. As far as the 1% / 70% .... any amount is considered Positive; no matter the percentage. When 1st and 2nd opinions are opposing you are entitled to a 3rd if you wish.. I would wait for the MDA report to be explained in detail though. Regards .....

[katarina777]

I know the FISH is a much more accurate, and much more expensive test, especially in determining Her2 status.

I don't get the part about calling your cancer nonspecific since I would think that obviously it is bc, just as your twin siters.