Has anyone experienced changing HER2 test results after breast cancer surgery?

Yes, my surgical path came back HER2 negative actually. My progesterone was much different too. It's my understanding from reading research that the cancer cells can be very different, referred to formally as heterogeneous. It's the nature of this breast cancer beast we are living with. My treatment continues to be based on my original biopsy (triple positive, 2.2cm, node negative) Since I had residual tumor, I did TDM1 for 14 cycles after my chemo and right mastectomy.

This kind of variation in HER2 testing results can definitely happen and understandably creates confusion during an already stressful time. Testing differences can occur due to various factors including tissue preservation, lab processing methods, or even differences between the original tumor and surrounding tissue. Many patients in this community have shared similar experiences with changing test results, so you're not alone in facing this uncertainty. Your medical team will likely use all the available information to determine the best treatment approach moving forward.