Oh no! I am sooooo sorry. Such horrifying news.
I wish that I had words to comfort, words to soothe...but none are sufficient at a time like this. All I can offer is my sincere sympathy and sadness for you and my prayers that Buddy will fully recover, soon.
As far as your question, I am not aware of Labradoodles being any more at risk for cancer than any other species...it is a horrible disease, striking randomly, and devastating the loved ones of those stricken.
I have been blessed not to have an experience in this, so I am not able to say what is likely...if you feel like sharing more details, perhaps one of the regulars on this forum (many are in the health field) will be able to give you more answers.
Have you notified your breeder? I believe that they would like to know. I don't believe that cancer is a genetic disease, so the health warranty probably won't cover this, but your breeder can be a great comfort to you if he/she is a compassionate individual. He/she will share your concern and fears...and sometimes that is a little bit of help.
Bless you, and bless little Buddy.
