Her2 positive for dummies - can someone explain in easy to understand terms?

[skoolmom]

I have had lots of people ask me what exactly Her2 is and what the positive is and what does Herceptin do to it. I really stumble when I try to explain it other than it's an aggressive cancer that's overproducing. I know that ER/PR is an estrogen driven cancer but mine is negative, and it's the Her2 that drives my cancer I guess? Hopefully someone can explain it in Her2 for dummies terms! I feel so dumb not knowing it exactly for myself! Thanks for all your help!