Ok - good news
Vet rang and spoke to OH whilst I was on my way home from work (am please cos Nurse said he was solidly booked and it would be after surgery when he rang!)
Firstly there are no cancerous cells
Unfortunately I can't make head nor tail of OH's spelling but apparently its a ? cyst, which is a waxy ? build up from the ? gland (inside the skin). It may get bigger but there is nothing to worry about