Question: What is HER2, how is it tested, and is it tested on invasive and non-invasive breast cancer?
Answer:HER2 is a protein that is found in about a quarter to a third of breast cancers. It is a signal that the cell has a higher tendency to divide because it actually is of a family of proteins that are receptors. Not for estrogen, like estrogen receptors, but for other molecules that signal growth. When HER2 is found in a cancer, it means that the cell is responding to those signals because, in general, that whole family of molecules is activated. This is important for several reasons. One, it tells us how rapidly growing the tissue is, which helps us plan therapy. But also, because we actually have a drug that can attack HER2 and can inhibit the growth of these cells; and that drug is called trastuzumab (or, Herceptin), is given intravenously, and has a profound effect at inhibiting the growth and often killing cells that have too much HER2 in them.
We look for HER2 in pre-invasive (or non-invasive) as well as invasive breast cancer, because it does help us plan the treatment in these cases. Trastuzumab (or, Herceptin) works best when it's given with cancer-killing drugs, certain chemotherapies, and it has been a very significant advance. Now we measure HER2 by looking at the tissue in several ways. We can actually look at how much protein of HER2 there is in the cell; all cells have some HER2, but these cancer cells have too much or an abundance of HER2. But we also can look at the DNA that signals the cancer cells to make too much HER2 -- that's called amplification -- and that's often a very accurate way for us to tell if that cell is HER2 dependent. But many other ways are in development now, and our technology in this regard is improving rapidly.
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