Hi Pammy
This is Kathy from BCNA's Policy Team. Sorry to hear you have been recently diagnosed with breast cancer. Breast cancer doesn't generally change from HER2- to HER2+. However as primek said, sometimes the diagnosis may change when the pathologist tests the tumour after the breast cancer surgery. The results may be different from the biopsy results as the biopsy only samples a very small number of cells. It doesn't mean the cancer has changed, just that there weren't a lot of the HER2+ cells in the biopsy sample.
As Afraser said, sometimes when breast cancer spreads to other parts of the body, it may have a different pathology to the early breast cancer - HER2+ instead of HER2-, or ER- when the early breast cancer was ER+. But this is not your situation.
Let us know if you have any other queries. All the best with your treatment. The women here will be a great support to you. So will a breast care nurse, so if you haven't seen one you should ask your doctor to organise that or call us on 1800 500 258 and we can help connect you to one in your area.
Kathy