Tumors can grow in the glands and lymph nodes of a dog's colon, resulting in colon cancer. There are two main types of canine colon cancer. The first is adenocarcinoma, or cancer of the apocrine glands, and the second is lymphoma, which is cancer of the lymph nodes. Though colon cancer can be treated to help a dog live a more comfortable life, the disease is fatal. Early detection is the best way to help your dog receive successful treatment, so it's important to monitor any symptoms that appear. Take your dog to the vet if any of these symptoms recur or worsen.