HER2 - IHC & FISH

My Mammogram showed left breast 2 clusters of microcalcifications and US not detected. Stereotactic hooked wired biopsy confirmed one cluster to be DCIS and the other DCIS+IDC. IHC HER2 3+.  Undergo Lumpectomy and during surgery found one lump 1.5cm and lymph node 2 out of 9 affected, IHC show HER2 3+. 3 weeks later undergo mastectomy, the IHC showed HER2 1+.  All showed ER and PR + by IHC. Requested lumpectomy tissue sample sent to another hospital to carryout FISH test and it show negative. My Question: Can it be the IHC +ve was on IDC clusters and the FISH -ve was on DCIS cluster?

[PaulMD]

Hi there.

The more definitive test for confirmation if Her2 status is the FISH (fluorescence in situ hybridization) and it can be really possible that the tumor may indeed be her2 negative.  There are some controversies regarding the interpretation of IHC and usually the +2 results are sent out for FISH.  However, it is not common for a +3 reading on IHC to turn out negative on FISH but it does happen.  I suggest you discuss this thoroughly with your oncologist since the definitive presence or absence of the Her2 receptor will dramatically influence the management of the disease.  He may want to send other samples to FISH (like to wire biopsy specimen?).  Regards and God bless.