Welcome to the board...I'm so sorry that you've had so many horrible things happen, especially so close together. And a three year old dog dying is just plain wrong.
What did the breeder have to say about the type of cancer involved and his/her experience with that line? And do you trust him/her? I'd ask there before talking to the vet. Also, perhaps someone on here might know of the breeder....if you get your post count up (I think to 5), you can send and receive private messages. Posting breeder names in this public area isn't allowed but someone might post here for you to send them a PM to discuss further.
Good luck as you pursue a future puppy!