Cancers in dogs are quite often asymptomatic until the disease is well advanced. The large, air-filled nasal cavity in a dog's snout can be a good place for tumours to hide until they become visible and uncomfortable. By the time nasal tumours become noticeable, the cancer has often spread to other organs and become much more difficult to manage.
Nasal cancers in dogs, also called carcinomas, can consist of three different types of cells. Basal cell carcinomas are tumours of the skin that invade and destroy surrounding tissue but usually don't metastasise, or spread, to other areas in the dog's body. The more serious squamous cell carcinomas are normally found in mucosal tissue, such as the inside of the nose, and can become metastatic. Sarcomas are highly metastatic cancers of the connective tissue, such as cartilage, blood vessels and lymphoid tissue and can also manifest in the nasal cavity. The only way to make a true diagnosis of which type of cancerous cells are involved is by microscopic evaluation by a veterinary professional.
Medium to large male dogs over the age of 10 are more commonly affected by nasal cancer than are female dogs. Clinical signs may include sneezing, an inability to breathe, nasal discharge (either yellow, clear or bloody), tearing of one or both eyes and a distortion of the facial structure caused by tumour growth. Nasal tumours are more commonly seen in dogs with long snouts. Symptoms will usually present themselves on an average of three months before diagnosis.
Veterinary treatment of nasal cancer usually starts with surgery to remove the tumour and stop it spreading to nearby bone tissue. A microscopic biopsy will determine the origins of the cancer. A veterinarian will often recommend radiation therapy after surgery to prohibit further tumour growth. Ten to 18 treatments over two to four weeks will be directed to the affected area. If radiation therapy is not an option, chemotherapy treatment may be recommended.
Other diseases that can show the same clinical signs as nasal cancer include high blood pressure, allergies and fungal infection. Nasal discharge plus depigmentation of the nose is usually a clear indication of a fungal infection, but a diagnosis needs to be determined by a veterinarian, who can then recommend treatment.
About 80 per cent of nasal tumours in dogs are shown to be malignant. These cancers spread very quickly in the dog's body, most often to the bones, lymph nodes and lungs and, if left untreated, usually result in the death of the animal within 95 days, according to Dr. Stephen J. Withrow in his 2007 book "Small Animal Clinical Oncology." Dogs with a bloody discharge have been shown to have a higher incidence of metastatic disease than dogs with a clear or yellow discharge. According to Withrow, head of the Oncology Department at the Colorado State School of Veterinary Medicine, surgery without radiation will most likely result in a lifespan of three to six months after diagnosis, with 40 to 60 per cent of patients alive one to two years after radiation therapy alone. The best prognosis is for dogs that undergo a combination of surgery plus radiation, with survival times averaging four years.