I hate to say this, but every golden we have owned and has gone over the rainbow bridge, has passed away from cancer. Both died from Hemangiosarcoma at 10+ years. I have an eight year old female currently in remission after being diagnosed with lymphoma. She has been given six months to a year and her treatment was for free through a cancer study at UW Madison Veterinary school.
I am not looking to blame anyone for cancer in goldens because if you ever bred a golden litter, you might have produced a dog with cancer. Looking at field goldens in particular, there is very little genetic diversity. When you do a heavy line breeding to a certain dog(Joe Smoe) for a certain trait, you also get Joe Smoes bad traits too. Genetics, traits, hereditary only play one part of the equation. The other part of the equation is the environment. I have heard theories from carpeting to truck exhaust seeping into the truck bed causing cancer. It is important to know what causes cancer, but it is more important what will be done with the information in the future to secure the breed.
The biggest part about canine cancer is that there is not enough research to formulate an accurate thesis. Canine cancer overall is on the rise, labs included. If you have a golden with cancer or any breed for that matter, donate a biopsy for more research. If you are fortunate to get your dog into a study or a drug trial, then do so. I bred my eight year old female who has lymphoma and I wonder about the future or how many of her offspring will come down with lymphoma.