Gomez, I sure wish ya'll the best.
We went through something so similar with our hybrid wolf, but I can't rememmber the medical condition, wasn't cancer but a desease that causes all the orgens and cells to bleed.
While on a job out of town my wife mentioned "jasemine" was acting tired and depressed cause "dad" was gone so long. after 4 more day's I returned early Saturday morning and for the 1st time in 12 years I was not greeted with a howl.. tried all day to find a week end vet, went to an emergency clinic..Closed....(what the) she would try to follow me over the week end but couldn't so I stayed with her. Sunday after noon I had to run to the shop, I get home and hear my daughter screaming, ( she had taken "jassy" out for a bathroom break), I ran outside and Jasmine was lightly convulsing, I sat down, put her in my lap and began rubbing her face, I just kept telling her to go that it was ok, she died in my arms and I cried like a baby. Wasn't like loosing a child, but more, my most trusted friend.
Had an autopsy done, was nothing that could have been done. The quilt my wife and I felt was enormous, the what ifs etc tr..
That day was a heart ripper for sure, Jasmine has a special place by our house as she has had since she was born.
Till this day my daughter thought her "tough" ole dad didn't cry..
So I truly sympathize with you and your family and wish you the best during this ordeal, and I hope for a peacefull ending for your pet.