My mother has a growing pimple-like spot on her back with a tiny black spot in the middle. i'm concerned because it keeps growing.is it cancerous?

Maybe: In order to answer your question, a dermatologist would need to examine your mother. If you are worried, I suggest you make an appointment with a dermatologist in your area.

Unlikely: Needs to be seen by a physician but sound like a cyst. This sounds like a sebaceous cyst with stuff inside like cheese. It has a black center and will slowly get larger. May need to be removed but is benign. See the doc and get the answer.