Unfortunately cancer is relatively common in dogs. There is a much higher incidence of cancer in older dogs, although it is often diagnosed in dogs under two years of age. As scary as the word cancer is, it is important to remember that cancer is the most treatable chronic disease that animals get. Many cancers can be cured with surgery, some which chemotherapy and radiation therapy, and some need a combination of treatments. Common sites for cancer in dogs include skin, lymph nodes, bones, and spleen.