A single lump uder skin something like acne?

Patient: I’ve had this lump on the back of my shoulder for about 3-4 years. It’s the same color as the rest of my skin. It’s hard and sticks out in like a half a circle thing under my skin. I once poked it with a sterilized sewing needle and tried squeezing the white dry flaky like puss out of it but this didn’t work. It’s not painful, just bothers me. I tried 10% benzoyl acne gel on it but it doesn’t seem to help. I wonder what it is and how to treat it. Any suggestions?

Doctor: