Darker spot on Birthmark?

I had a birth MOLE on my chest since I was born which was a pinkish-orange color (I'm white, so it was close to my skin color). A dark brown spot started forming right in the center of it when i was like 13, but I never thought much of it. I wanted to get the mole removed, because it always showed when i was in my swimsuit (I'm a competitive swimmer) and it was ugly looking. The dermatologist was concerned about the mark in the center, and decided to take it immediately off because it could be cancerous. Please visit your local dermatologist and , I'm sure you have nothing to worry about, because he said my situation was rare. But just to make sure, ya know :) God bless, hope this helped :)