Young gyp dies mysteriously

Reuban, I just lost a 3 1/2 year old gyp. I only had her about 6 months. she came from Wisc. I noticed one day, she really had a bloody diarreaha & my first thought was Parvo but I have never had a grown dog get it. Took her to the Vet & he pulled blood & her white blood count was sky high. He put her on fluids & antibiotics but she died in two days. he did a autopsy on her & she had a large mass on her Pancreas going to her intestine. There are probably a lot of reasons why some dogs die but unless they are tested or Autopsied it is hard to find out why.