Cysts can also exist under the skin so check with your dermatologist. Cysts are generally benign but can transform and give malignancies. If not a cyst it could be lipoma which is growth of the fat tissue, also benign, but if it is lipoma it wouldnt be a boney lump. So get a clinician to take a look at it if your worried.
its under the skin though
Sounds like a cyst. I wouldn't worry about it being cancer but I would have a dermatologist take a look at it. Good Luck!!