This article is all about canine nasal tumors. As you'll learn, this is a type of cancer for which we've recently discovered a successful "new" treatment. This treatment is more successful and easier for patients than previous treatments, which is excellent. The treatment is not inexpensive, so another reason to have a comprehensive insurance plan for your dog.
Which Dogs Are Most Likely To Develop Nasal Cancer?
The average age of affected dogs is about 10 years, however dogs as young as 9 months have been reported. Long-nosed breeds (dolichocephalic) or dogs living in urban environments (filtering environmental pollutants through their nasal passages) are thought to be at a higher risk for developing nasal cancer. Exposure to second hand smoke increased the risk of developing nasal cancer in dogs in one study (not all studies support this). Exposure to indoor coal or kerosene heaters may also increase the risk of nasal cancer in dogs.
Which Types of Nasal Cancer Are Most Common?
Carcinomas (adenocarcinoma, squamous cell carcinoma, undifferentiated carcinoma) account for 60-75% of all canine nasal tumors. Sarcomas (fibrosarcoma, chondrosarcoma, osteosarcoma, undifferentiated sarcoma) make up the majority of the remaining nasal tumors.
Far less common tumors to affect canine nasal passages include lymphoma, mast cell tumor, hamartoma, leiomyosarcoma, hemangiosarcoma, multilobular osteochondrosarcoma, etc. Polyps, fibromas and other benign tumors can also occur in the nasal cavity.
Nasal Tumor Behavior
These tumors are typically locally invasive. This means that they destroy the nasal turbinates (small bones within the nasal passages) and can even invade through larger bones of the face/nose as well as through the cribiform plate and into the brain.
Although in most cases the tumors have not metastasized at the time of diagnosis (up to 24% have metastasis at diagnosis), up to 40-50% have metastasis at the time of death. Patients inevitably die due to the failure to control local disease in the nasal passages (and the effect that has on quality of life) as opposed to metastatic disease.
The most common organs of metastasis are regional lymph nodes and the lungs.
What Are The Most Common Signs of Nasal Cancer?
Many of the signs of nasal cancer are similar for benign conditions such as fungal disease, nasal polyp, nasal foreign body (in California we have foxtails). We are more suspicious of nasal cancer if the signs are noted in an older patient.
Typically patients will have a history of progressive one-sided epistaxis (nasal bleeding), which will be intermittent at first. They might only have nasal discharge (yellow/white in color) or they may have this plus nasal bleeding. They might exhibit sneezing, protrusion of one eye (exophthalmos - due to the tumor growing behind the eye and pushing it out), facial deformity (due to the tumor eating through the nasal bones and causing a mass effect), pain eating or opening their mouth (due to the tumor eating through the hard palate); their breathing might also become a bit noisy (air cannot pass through their nasal passages normally).
How Do We Make A Diagnosis?
A thorough workup is needed to obtain a diagnosis. Is the patient having nose bleeds due to a bleeding disorder? Fungal disease? Is there just inflammation of the nasal passages (rhinitis)?
Obviously, if there is severe facial deformity we will be much more suspicious of cancer, so we use our physical exam and clinical impression to guide us in recommending the most reasonable tests for the family.
Typically the BEST tests for diagnosing a nasal tumor include CT scan of the head followed by rhinoscopy with biopsy of the mass inside the nose. These tests are usually performed by an internal medicine specialist under anesthesia.
The CT scan will show a mass in the nasal passages as well as the extent of bone destruction. The scan will guide the internist so they know the BEST place from which to obtain their biopsy sample. After CT they usually move the patient to the endoscopy suite to perform rhinoscopy. This is where (still under anesthesia), they insert a scope (with a camera on the end) into the nasal passage. They obtain a few biopsy samples using the assistance of the camera. A few days later, they (or the oncologist) call the family with results.
If rhinoscopy is unavailable, blind biopsy can be attempted to procure a sample, but this is typically less favorable.
To assess for metastasis, the lungs should be evaluated with either 3-view thoracic radiographs reviewed by a radiologist, or CT scan. The mandibular lymph nodes should be sampled to rule out lymph node metastasis.
What Is The Prognosis Without Treatment?
The prognosis without treatment is influenced by whether the dog is experiencing nasal bleeding. One study showed that the MST (median survival time = half live longer, half do not live as long) for dogs that had nasal bleeding but did not receive treatment for their cancer was 88 days from the time of diagnosis. For dogs that did not have nasal bleeding, the MST was 224 days. It's not uncommon for dogs to have signs for months before a diagnosis is actually made.
Surgery is not typically advised for this disease. Tumors have typically invaded into the bone at the time of diagnosis, at which point surgery does not seem to provide benefit. One study showed that the MST was 3-6 months for dogs undergoing surgery, which is similar to the MST for dogs not receiving any treatment. If a tumor was very small and not invasive, surgery followed by radiation (see below) could be considered.
Surgery can be considered for nasal hamartoma and lesions that are not invasive.
Radiation therapy is considered the gold standard treatment for most nasal tumors. There are different types of radiation therapy and numerous different radiation protocols. Traditionally, survival depends on how well the patient responds to treatment (Has radiation completely eliminated the tumor?) and how advanced their disease is at the start of treatment (Has it invaded into the brain? Is it affecting the left and right nasal passages?).
The most conservative type of radiation is called palliative. This involves just a handful of treatments either given once weekly or all within one week (based on the preference of the radiation oncologist). Sixty-six percent to 100% of patients will have an improvement in clinical signs (less nasal bleeding, less sneezing, feel better, etc.). These patients have been reported to have an average length of tumor control of 120-300 days and a MST of 146 to 300 days (results vary widely between studies). If palliative radiation was successful, it can often be repeated a second time (if enough time has passed between treatments). If the patient's eye was in the treatment field, they may experience chronic dry eye and require lubricating drops indefinitely to avoid corneal ulceration. If the tumor is very advanced, we can initiate chemotherapy after radiation is completed in an attempt to better control the tumor.
If a more traditional, definitive (full course) radiation protocol is administered, consisting of small daily doses of radiation for about 19 days, 46% of patients will experience 90% reduction in the size of their tumor for 389 days; patients that experienced less than a 90% reduction in the size of their tumor had tumor control for 161 days.
If an excellent response was noted with the first course of radiation, a second course can be administered (typically a full year must pass in between treatments); one study showed that a group of patients lived 927 days when treated with two full courses of definitive radiation therapy.
Recently, more patients are being treated with SRT (stereotactic radiation). The benefit is that in just three consecutive daily treatments, SRT can deliver a very targeted and relatively large dose of radiation to a nasal tumor. This seems to result in excellent response rates and minimal side effects. A recent paper showed that the MST was 586 days for dogs with nasal tumors treated with SRT; SRT prevented patients' tumors from progressing for an average of 354 days. This outcome is superior to what is gained from the other types of radiation, in fewer treatments. In many cases, we will repeat a CT scan a few months after SRT to gauge our success and the tumor will have been completely eliminated. We still have to monitor for tumor recurrence, but these dogs can do (and feel!) very well.
The other very significant difference with SRT is that there does not appear to be a shortened survival (lifespan) for patients that have more advanced forms of the disease (if the tumor is invading into the brain, for example). SRT is becoming the treatment of choice for canine nasal carcinoma.
Radiation cost varies based on the type of radiation being pursued and the families' location (academia vs private practice, HCOL vs LCOL region, whether the family has comprehensive pet insurance. Possible side effects from radiation vary based on the type of protocol pursued and the extent of tumor involvement (big radiation field vs small field).
If radiation is not available or not elected due to financial constraints, chemotherapy (CCNU, carboplatin, Palladia, etc. - it depends on the type of cancer) can be used in an attempt to shrink the nasal tumor.
Dr. Lori Cesario
Board Certified Veterinary Oncologist
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(1) Dog Breeds and Their Associated Cancers
(2) Mast Cell Tumors - The Great Imitator in Canine Cancer
(3) Canine Splenic Tumors - What You Need To Know
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