Lump on my mare, anyone seen anything like this before?

[showjump]

(Also in breeding)
Hi noticed this today when washing my mare off after being ridden, i have never noticed it before and have never come across anything like it. Mare is 5 years old, bred a filly whos now 16 months old.
Any advice please, she doesnt mind you touching it. It feels hard and as though it is just under the first layer of skin.
Its just to the side of her teats, towards the back, if that makes any sense.

 

[JessandCharlie]

Could it be a melanoma?

 

[brighteyes]

Is it a sarcoid? Maybe get a vet to look but certainly a) don't mess with it and b) keep a close eye on it.