Guinea Pig Cancer

Question
My husband and I had our guinea pig (Mr. Pickles) for about 3 years.  June 1 he became very sick.  We rushed him to the vet. They thought he may have a blockage or twisted intestine but during surgery found cancer (of the intestines).  The vet said euthanasia was the kindest thing to do.  We didn't want him to suffer so we followed the vets advice.  
We are devastated.
I have read that cancer is rare in guinea pigs...so now I'm wondering if we were doing something wrong.
We gave him Nutriphase Gold (guinea pig food mix)morning and night feeding, a salad of Romaine lettuce, baby carrot, quarter orange, and small piece of apple every night.  He had Timothy hay at all times.  Afternoon snack of either romaine or baby carrot. And fresh water every night with Vit. C drops.  
He loved cardboard so I bought the big Chub tubes for him to chew on.  
He was very active and seemed happy right up until the morning of his death.  
Should I have not given him the cardboard?
Do you think that is what caused this or was it what I was feeding him?
Thank you,
Theresa  

Answer
It could have possibly been the cardboard, however, most guinea pigs will chew on cardboard, but not ingest it. So the possibility of that being the cause is very small.

The food you were feeding him was fine. Nutriphase Gold is a popular brand food that many people use.

Other than that, it sounds as though you were doing everything perfectly, right down to the water, veggies, and hay. I can honestly say that it really doesn't sound like anything you did was the reason for his illness.

Hope this helps!