Lipoma grew and hardened

My dog had this lipoma which has been previously checked by our vet. Recently it's grown and gotten quite firm, wondering if this is a bad sign. Vet appt this afternoon 

Hello!   I agree that it's something to be concerned about.  You don't mention to what level it was checked by the vet - if it looked like a benign lipoma and no tests were done (or an aspirate that showed a few fat cells) but it has changed, then many vets would be wanting to fully biopsy at this point.  It doesn't necessarily have to be sinister - it may be a cyst or a benign tumour, but it may be wise to find out.   If it is absolutely known to be a lipoma, then there may be a discussion to be had about dietary treatment.

Your vet will usually examine the lump and then make a decision as to where to go from there

Your vet will usually examine the lump and then make a decision as to where to go from there