My dog as a kid got a tumor right in his 'arm pit' of his front leg. He had a surgery, they successfully removed it and he lived another 5 or so years.
At 16 he started to get more tumors. All over his body. Back, legs, even one on the top of his head. Doctor said they were fatty tumors. A year later at 17 he started to get arthritis so bad he couldn't move, and we had to put him down because he was so miserable. He couldn't even get up from a prone position without help. We couldn't bear to see him suffer anymore. Hardest decision my family ever had to make.
Hard to believe an outdoor dog lived 17 years. He was tough, hated the house. He would come in for 10 minutes and start banging on the door to go out. He was elk hound border collie.