does all people have cancer cells in their body?

I have heard of this one too, I don't really know if it's true. I was told that cells turn into cancer cells all the time but most of they switch again and go away, it's only sometimes when they don't do. I'm not sure if that's true, but appreciate you rising the question, would like to know more!

Not exactly,i think what you meant is proto-oncogenes,which exist in the cells under normal condition,they play an important role in the growth and differentiation of cells.but due to abnormally increased expression,mutations or translocation,they may help to turn the a normal cell into a cancer cell which aslo be called tumor cell,this is the basic process of tumor generation.