HER2 +/-

How common is it for the tissue samples from a core needle biopsy to show HER2 negative and then show positive after the lumpectomy tissue is analyzed?  

[PaulMD]

Hi.

This scenario is indeed possible and I have seen this personally a lot of times.  Core biopsy only samples a small portion of the entire tumor.  Since the cancer tumor is heterogenous (meaning, not all cells are exactly alike), it may be possible that the core sample does not harbor Her2.

Since the lumpectomy removes the entire tumor, areas of Her2 positivity will really show up on examination.

Regards.