Why HER2 +/- Changed

Rose88 Member Posts: 2 Member
edited May 2023 in Breast Cancer #1

Hi all, I was diagnosed with stage II breast cancer with two lymphnodes involved in Oct 2022..... PR negative, ER weak positive and HR2 borderline positive (and FISH test confirmed HER2 positive in Oct).

With that diagnosis, I received Taxel and HER2 target drug Herceptin and Perjeta as neoadjuvant therapy before the mastectomy in April 2023. Biopsy from the removed cancerous tissues again showed PR negative, ER weak positive and HER2 borderline positive. But this time, to my surprise, FISH confirmed the HER2 is NEGATIVE. 

I am very confused by the HER2 change from positive to negative in such a short period of time (less than six months) and worried about the focus of my adjuvant chemo treatment.

Does anyone else have any experience with this situation? What is the reason causing the change? Did you do any additional testing to reconfirm?  How did this change affect the course of your treatment plan such as target drug change etc?

Any help would be greatly appreciated.


  • EmilyG
    EmilyG Member Posts: 2 Member

    I have not had that situation yet but I am expecting it soon. After several biopsies and tests, I was diagnosed ER+ and PR+ in both breasts and had a double mastectomy in early May 2023. The post surgery pathology report states that I am HER2+ and they ordered a FISH test. Waiting on the results but I am wondering how these things also changed in less than a month. Sending you good luck and hugs.

  • Rose88
    Rose88 Member Posts: 2 Member

    Emily, thanks for your comments. My doctor switched me to target drug Kadcyla/TDM1 after the surgery. I am still not sure what caused my HER2 positive/negative change but follow the doctor's treatment plan. Hope you get satisfying explanation from the FISH test. Wishing you all the best.