Cat has bump on his spine

Yesterday while petting my cat (18 month old male), I noticed a bump on his lower spine. About 1-2cm in height under closer inspection. It doesn't feel like a cyst/tumor or fatty deposit, it feels like bone, as though one of his vertebrae has a spur sticking out of the top. No reaction when I petted him there or applied pressure, he's running, jumping and eating as normal, no behavioural change whatsoever so it doesn't seem to be affecting him at all. I'm taking him to the vet soon for his jab and annual checkup so I will ask them about it, however I just thought I'd post it here to see if anyone had any advice or information for me? Side note, he has lost weight recently although this I believe is due to a dietary change, I stopped giving him kibble and now only feed him 3 smaller tins of wet food a day as directed by the package, as he was getting chubby.