Why are some of us HER+

Hi all, have we worked out yet why some of us are HER+? I have been on Herceptin for about 3 years or more but during this time out of all the people tested I am now the only one on it at my hospital oncology, the other 2 ladies died because they were not put on it earlier in their treatment , it was not available at the time, so it was not a benefit. Do we have anything else in common with each other.

Love & Hugs Lyn