Bump on my guinea pig

[Opiggy]

I posted about this a few years ago, and I have continued to watch it. The bump has grown a lot in size in the past 2 years. However, he seems to be just as healthy and of course I think if it was something bad like a tumor it would have affected him by now.
Here is the before and after

 

[weepweeps]

Whereabouts on his body is the lump?

 

[Merab]

Have had the lump checked by a vet ?

 

[Opiggy]

It’s behind his ear and has not been checked by a vet

 

[Merab]

If it’s growing a vet check may be useful.
It will reassure you if this is just a harmless lump