When our little shitzu died at 13 from cancer in 2007 our vet said he was seeing much more cancer in dogs - up from one maybe a month to several a week. He really felt it was something to do with dog food as so much of it is produced in China and other countries as opposed to the US. He said even if made in US a lot of the ingredients came from other countries. He said it was just his opinion but I have a feeling he was really onto something.
Vaccines, vaccines and MORE Vaccines!