Cat has inverted nipple and buildup inside?

I need some advice from someone who works with cats until I can get mine into a vet. My cat has a small lump on her chest so I checked it out and the nipple was inverted and there was a white build up (not runny like a discharge) that comes when you squeeze it. She has had this before and the vet kind of dismissed it and I was wondering if this is dangerous and what I need to do to help her.