Cancer is like a ticking time bomb, once you have it you know that your life is near. Those stricken with cancer lose hope in life and would want to end their suffering at the soonest possible time.
This is also true in dogs suffering from cancer. When Wallace was diagnosed with a commonly occuring cancer called hemangiosarcoma, they know that their dog's end is near. Wallace was given two to three months of chemo-free diagnosis, then after that it's the end. But miraculously, Wallace managed to survive cancer! In fact, Wallace has gone through his 11th birthday and was able to survive for 7 months chemo-free! Now that's a miraculous recovery.
Because of that, the owners decided to give Wallace a birthday that he truly deserve. Just look at the excitement and joy of the dog in the video!