Lymphoma stands out as the type of tumor most commonly diagnosed in dogs. It often presents in the peripheral lymph nodes under the jaw, behind the knees, and ahead of the shoulders. These cases often present with minimal to no systemic symptoms other than possible lethargy and loss of appetite, but instead attract the attention of owners in the form of visible tumor growth and swelling.
Lymphoma may also develop in dogs as an internal disease. When it grows inside the chest cavity, the dog may experience shortness of breath, and a veterinary exam is likely to reveal diminished heart sounds. Dogs with lymphoma in the digestive tract, by contrast, more often present with such gastrointestinal symptoms as diarrhea, vomiting, and weight loss.
In general, the prognosis for a dog with lymphoma is significantly better if the cancer is confined to a single node or, failing that, a single region. Dogs with a more systemic presentation of the disease typically have a four- to six-week life expectancy without treatment, though targeted therapies may give a dog up to a year of life.