[Becky]

What happens is that the gene for Her2 (we have 2 of them - one on each of the pair of chromosomes (I think its located on Chromosome 17 but I am not sure). Somehow, the cell divides wrong and (let's say), instead of 2 chromosomes in each (of the new cells), 3 are in one cell and 1 is in the other cell. Perhaps the cell with one chromosome can't "make" it (unless it got 3 chromosomes of something else (lets say the gene for the estrogen receptor (ER)) but the cell with 3 does and it reproduces and divides wrong again (I think you get the picture) and then you have surviving cells that have too many copies of the Her2 gene (this is what the FISH test tests for). Too many copies produce too much protein (this is what the IHC test tests for). The same reproductive prinicipal holds for ER, PR, Her1 etc.


Remember too that other genes are located on these chromosomes too and chromosomes can "swap" pieces of themselves during the reproduction process. This is why we are all so unique AND our cancers are actually unique too (like snowflakes, none of our cancers are alike - nor are we). I hope this is clear enough. Let me know.

For the record - cells that don't have the right amount of chromosomes are called aneuploid.

PS - all cells have the Her2 gene. Ovarian cancer can be Her2+ too but Herceptin doesn't tend to work well on them. Many, many forms of cancer are Her1+ (aka EGFR).