9. Strange odors
Foul smells could be emitted by dogs with cancer because often a tumor will cause a blood clot, or press against nerves which will in turn die off due to lack of circulation. The dead area will begin to rot and a foul smell will soon become more prominent, (it will often be in the area near the nose). This is similar to how gangrene affects humans. There may be surgical options at the vet, but this is a fairly advanced sign of cancer, so it would be better to catch the cancer before this symptom occurs.