Lani

Could you please provide the source of your reference to 20% of her2+ patients becoming negative once they metastasize. (I may have read you wrong, but I assumed you meant that their mets were negative for her2 whereas their primary was her2positive) I think you may have this wrong, as I have read that contrary to Estrogen receptor, where mets from ER positive patients may be ER negative and mets from her2negative patients that may be her2positive. that "once her2positive, always her2positive" ie, if primary her2positive than mets her2positive. This has to do with what was discussed at length during questions after talks at SABCS--whether the ER is present on breast cancer stem cells (or only on the progenitor cells) or not. It has been felt by Max Wicha and others that her2 is likely present on stem cells--thus the primary tumor may represent a quickly dividing/growing group of more differentiated progenitor cells where as the mets come from the previously dormant stem cells .

This has been important in a very interesting and frightening paper I found
on the prognostic significance of her2 positive isolated tumor cells in bone marrow (ie, they did cytokeratin AND her2neu double staining ) by IHC.

Will try to search for that article and post it for you

Lani