Just as I was so pleased & relieved that our problems with cystitis are over and Razbeg's bloodwork results were excellent, I noticed a lump/swelling on his remaining front leg. It's on the backside of his leg, below the carpal joint and next to the dew claw (which he doesn't have, but where it would be). It moves horisontally and is about the size of a thumb. Doesn't seem to be sore when touched & Razbeg has behaved normally on walks, but he's on pain medication anyway and as it's his only remaining front leg, so I don't know how he would show the pain (other than refusing to walk altogether). Unfortunately I can't go to the vet today, as I have to go to work. Tomorrow they have emercency duty and I could go there and hope they can meet us at some point, but as he doesn't seem to be in pain, I wonder if I could wait till monday.

But my question is, what could it be? I have tried to google what's in that area, but I don't know. Could it be something to do with extensor tendons? Sign of carpal hyperextension? Or what I'm afraid of, could it be the cancer popping up in a new place? Is there some muscle in that area that could be swollen? I would just want to hear some possibilities while waiting to go to the vet, as I'm quite nervous about this.

Razbeg is borzoi, 11-years old male and weighs about 25 kg (55 lbs).

I would really appreciate some insights into what could it be & thank you in advance if you can provide them