I have a lump behind right ear for 1 year. ent described it as a bony mass and recommended biopsy. i declined as hadn't grown much. right decision?

Bony Mass: If this is associated with hearing loss, I STRONGLY recommend a CT scan to see if there is an infection or growth affecting your hearing.

Probably: But would need more info. There are bony prominences behind the ear that are normal. Though I'm not sure why ENT would want to biopsy those. If this is a different mass then biopsy would confirm a diagnosis for you. Have you had any imaging. Often a simple X-ray or Ultrasound can help diagnose these. Stability ( no change) over a year is a good sign that it's benign ( but no guarantee )

Well: Best to fill low the recommendation of your doctor since it seems to have grown. Reconsider your decision and go back to doctor