How would you manage adjuvant therapy for a premenopausal female with a T1cN1mi breast IDC that is HR+ HER2 positive on biopsy, but HR+ HER2 negative on lumpectomy surgical specimen?

Overall, I agree with Dr. @Dr. First Last's response regarding treating this as a heterogenous tumor, but I would probably lean towards 4 cycles of TC (docetaxel/cyclophosphamide) for the HR+/HER2 neg component and then add 1 year of trastuzumab. This would avoid the risks of anthracyclines and pert...

HER2 testing is overall borderline and would be considered positive by the biopsy and negative by the surgical specimen when both IHC and FISH results are taken into consideration. HER2 FISH testing result falls into Group 3 and is similar in both specimens. In Group 3, HER2 is currently deemed posi...