First, the good news: most people are not buying breeds with a high prevalence of bone cancer, i.e. osteo sarcoma.
The bad news is that bone cancer is quite common in greyhounds and many extra large breeds.
Nationwide Pet Insurance, formerly VPI, aka NationwideDVM, has produced a nice new study on the prevalance of Osteosarcoma in dogs. Check it out!
Bottom line: "the most reliable predictor of a higher prevalence of osteosarcoma is the size and/or breed of a dog." Thanks to Gina Spadafori for sending this to me -- nice work from Nationwide!