Growth/lump on dog

Hello, I noticed this growth on my dog a week and a half ago. The 1st picture is yesterday and the 2nd picture is a week and a half ago so it’s definitely changing. I am going to get him booked into the vets but I’m worried it’s something serious. I was just looking for some advice or ideas on what it may be? Thank you  

Hello - there are both concerning and non concerning possibities as to what this lump might be.   There is a thing called a histiocytoma that springs up and goes down on its own; there are foreign bodies; there are cancers.  Your vet will not necessarily be able to tell you when they see it either.  However, they should help ypu to make a decision; is this something best investigated, treated or left alone?

I'm just coming back to say that this could be the remains of the umbilicus (tummy button); if it's quite central and there isn't another.  If so, it looks to be herniated slighty and again, needs to be checked by your vet.