Nasal adenocarcinoma is characterized by the slow, progressive, local infiltration of tissue lining the nasal cavities (sinuses) by cancerous glandular epithelial cells. Most nasal adenocarcinomas in dogs are unilateral at first, which means that they usually start on one side of the nasal sinuses. However, nasal adenocarcinoma usually ultimately becomes bilateral, involving both sides of the nasal cavities. About 20% of these tumors start in the dogs' frontal sinuses. Adenocarcinoma is the most common cause of neoplastic nasal disease in domestic dogs, being more common than fibrosarcoma, chondrosarcoma, squamous cell carcinoma and other forms of nasal cancer. Still, nasal tumors are not especially common in canines.
Causes of Nasal Adenocarcinoma
Despite intensive research in both animals and humans, medical science has not yet discovered the precise causes of the various forms of adenocarcinoma, including the locally invasive and usually metastatic nasal adenocarcinoma. Chronic exposure to environmental pollutants has been suggested as a possible contributing factor in dogs that spend the majority of their time in urban settings. Exposure to secondhand smoke (from cigarettes), wood dust and/or toxins from the boot-making or flooring industries have all been weakly linked to nasal tumors in domestic dogs.
In a more general sense, almost all cancers are "caused" by cellular reproduction and tissue growth that occurs at an accelerated, uncontrolled rate. Normally, most cells in the body have a predetermined life span and, when they die, are replaced in an orderly fashion that is controlled by the dog's genes. When something disturbs this normal genetic process, cellular mutations can occur. These mutated cells tend to reproduce at an alarmingly fast rate, without normal regulation. They can accumulate in masses, called tumors, which can crowd out normal cells and impair normal bodily functions simply by their space-occupying presence.
In addition, cancer cells are no longer able to perform the functions that their normal predecessor cells did. As they continue to multiply without pattern or purpose, the offspring cells similarly lack the capacity to perform normal cellular functions. Cancer cells can enter the dog's blood stream and/or the lymphatic circulatory system and travel to remote sites – a process called metastasis. They can lodge almost anywhere in the body and continue to reproduce uncontrollably, causing progressive tissue damage and destruction.
In addition to a dog's inherent genetic makeup and possible genetic mutations, there are environmental carcinogens that can increase the likelihood of cancer in our companion animals. Carcinogens can be eaten (ingested), inhaled or contacted physically, causing eventual alteration in the dog's genetic code and disrupting the normal system of checks and balances that controls orderly cellular function, growth, reproduction and death.
Prevention of Nasal Adenocarcinoma
Because the cause of nasal adenocarcinoma is not understood, it is virtually impossible to describe a meaningful prevention protocol. Unfortunately, little is known about how to prevent any type of cancer in companion animals.
Early diagnosis almost always improves the prognosis for a dog with cancer. When an owner notices a lump or bump on his dog's face, an abnormal protrusion of one or both eyes, spontaneous nosebleeds for no apparent reason or otherwise perceives that his buddy just "isn't doing right," he should take his pet to the veterinarian for a thorough check-up as soon as possible. With prompt diagnosis, aggressive treatment and ongoing management, dogs with nasal adenocarcinoma may go on to live comfortably for months to years.
Adenocarcinomas can affect a number of glandular organs in domestic dogs in addition to tissue in the nasal cavities, including: salivary glands, thyroid glands, lungs, pancreas, kidneys, skin (sweat glands, sebaceous glands), stomach, small and large intestines, rectum, anal sacs and prostate glands.
The symptoms of canine adenocarcinoma will vary depending upon which glandular tissue is affected, the severity and extent of infiltration and metastasis and the dog's overall systemic health - especially the functional strength of its immune system. Nasal adenocarcinoma tends to show a fairly consistent constellation of clinical signs.
Symptoms of Nasal Adenocarcinoma
Nasal adenocarcinoma usually involves the slow, progressive, local invasion of the lining of the nasal cavities by neoplastic glandular cells. Typically, one nasal cavity is affected first, and then the other becomes involved. Symptoms may include:
Nasal discharge – unilateral and/or bilateral (coming from only one or from both nostrils); +/- mucus and/or pus (mucopurulent nasal discharge); +/- fresh blood (hemorrhagic nasal discharge); +/- thin, watery (serous) nasal discharge
Nose bleeds (epistaxis) – intermittent and progressive; unilateral and/or bilateral (coming from one or both nostrils)
Excessive tearing (abnormal overflow of tears; epiphora)
Malpositioned eyes (abnormal protrusion or bulging of the eyes; exopthalmos)
Sneezing and/or reverse sneezing
Bad breath (halitosis)
Lack of appetite (inappetance; anorexia)
Seizures (with metastasis to brain tissue)
Facial deformities (space-occupying masses; bony changes)
Deformation of the hard palate
Deformation of the upper jaw (maxilla)
Pain (especially on nasal sinus examination or when the mouth is opened)
Blocked nasal passages (obstructed nostrils/nares)
Difficulty breathing (dyspnea) through one or both nostrils (physical airflow obstruction)
Enlarged lymph nodes (especially mandibular lymph nodes)
Dogs at Increased Risk
Mid-sized to large breed dogs appear to have an increased risk of developing nasal adenocarcinoma, and there also may be a slightly increased risk in males, although the reasons for these reported predispositions are not well-understood. As with many types of cancer, older animals are more commonly affected.
Nasal tumors are not particularly difficult to diagnose. However, it is important to determine the type of tumor involved, so that an appropriate treatment and management protocol can be formulated.
How Nasal Adenocarcinoma is Diagnosed
The results of routine blood work (complete blood count and serum biochemistry panel) and urinalysis are typically normal in dogs with nasal adenocarcinomas. Most veterinarians will take swabbed samples of nasal discharge and submit them to a diagnostic laboratory for evaluation, including microscopic assessment of the cells in the samples (a process called cytology) and possibly for bacterial culture and sensitivity. If the dog presents with a history of spontaneous nose bleeds of unknown origin, the veterinarian probably will also conduct a coagulation profile, to see whether there are any identifiable primary disorders in the dog's ability to form normal blood clots. This likely will include a bucal bleeding time test, which can easily be performed in-house at the local veterinary clinic.
More advanced tests include survey radiographs (X-rays) of the skull, to look for asymmetrical destruction of the nasal bones (nasal turbinates), facial bones and/or for soft tissues masses. Chest radiographs may be recommended to look for metastasis to the lungs. Much more advanced diagnostics may include computed tomography (CT scan) and/or magnetic resonance imaging (MRI), each of which provides a more sensitive assessment of the extent of abnormal tissue. A procedure called rhinoscopy can be performed to visualize the lining of the nasal sinuses and to enable the veterinarian to take tissue biopsies of any fleshy masses or other tissues that appear to be abnormal. This can be a tricky process, especially if a lot of blood or other nasal secretions are present. Biopsy samples will be sent to a diagnostic laboratory for definitive determination of the presence or absence of adenocarcinoma. Aspiration of regional lymph nodes – especially the mandibular lymph nodes – may reveal the presence and spread of primary nasal adenocarcinoma. Approximately 10% of cases have metastasized to regional lymph nodes at the time a diagnosis of canine nasal carcinoma is made.
There is no one diagnostic protocol for nasal adenocarcinoma. The veterinarian will adopt an appropriate diagnostic plan based on how the particular animal presents. However, adenocarcinoma is not particularly difficult to diagnose, if the owner is willing to go through the steps necessary to reach a definitive diagnosis.
Nasal adenocarcinoma can be tricky to treat. In many cases, it can be managed, although complete cure is rarely accomplished. Therapeutic goals include alleviating discomfort, preventing further metastasis, removing as much cancerous tissue as possible and prolonging the dog's good quality of life.
If a dog is having recurrent uncontrollable nose bleeds (epistaxis), immediate medical treatment may include sedation, packing of the nasal passageways with gauze soaked in medication and application of cold compresses to the dog's nose and muzzle. Antibiotics are available if secondary bacterial infection is confirmed, and either steroidal or non-steroidal anti-inflammatory drugs may be recommended.
Surgery is the treatment of choice for many canine cancers. However, surgery alone is rarely effective to treat nasal adenocarcinoma, because it is virtually impossible to surgically resect all abnormal tissue in the small, confined spaces of the nasal cavities. Certainly, much of the localized affected tissue, including affected turbinate or other facial bones and the tissues that line them, can be surgically removed, either before or after radiation treatment, depending upon the location and severity of cancerous infiltration. The biopsy samples from any surgical excision will be sent to a diagnostic laboratory, where skilled veterinary pathologists will examine the samples grossly and then microscopically to determine the exact type of cancer and whether appropriate surgical margins were obtained. When a focal cancerous mass is removed, the surgeon tries to also remove a small amount of normal tissue around the entire mass of abnormal tissue, in order to achieve what are called "clean surgical margins." If normal, non-cancerous tissue can be seen microscopically and continuously at and around all edges of the removed cancerous mass, the animal has a greatly reduced risk of metastasis from that tumor site. Unfortunately, this is usually not possible in cases of nasal adenocarcinoma.
Radiation therapy, both internally (called brachytherapy irradiation) and/or externally (teletherapy or external beam radiation), can be used to treat nasal tumors. This type of therapy is designed to kill malignant cancer cells in a defined physical area by exposing them to high levels of deadly radiation. These procedures are usually done daily for several weeks or more and thus are best done on an inpatient basis, with the dog staying in the hospital or with the owner nearby for the duration of treatment, monitoring and supportive care. Radiation treatments are usually well tolerated by most dogs and can prolong survival and improve quality of life. They are available at most veterinary teaching hospitals and at some specialized private veterinary referral centers.
Chemotherapy (treatment with drugs, either intravenously or orally) may be another option for dogs with nasal adenocarcinoma. Chemotherapy is a different way to kill cancer cells. It cannot target a specific physical area of neoplastic cells, but instead travels throughout circulation to target all rapidly-dividing cells in the body. Because of this mode of action, "chemo" is not as effective as radiation treatment for nasal adenocarcinoma. Chemotherapy reportedly may relieve the symptoms of nasal tumors for a number of months, but is not expected to cure the condition or increase survival time overall.
In some cases, veterinarians may recommend a combination of therapies, such as surgery together with radiation and/or chemotherapy. One of the adverse effects of both radiation and chemotherapy is that many normal cells are damaged or destroyed by the treatments. Other existing and emerging treatment options for animals with cancer include targeted molecular therapy, immunotherapy, hyperthermia, cryotherapy, phototherapy, photochemotherapy, thermochemotherapy and other emerging unconventional or alternative therapies. Most of these newer approaches are still not widely available in veterinary medicine. However, they may be worth discussing with a veterinarian as a potential adjunct to more traditional medical therapy.
The goal of treating cancer, of course, is to eliminate only the malignant cells. Unfortunately, it is not presently possible to completely isolate healthy tissue from cancerous tissue during these surgical, radiation or chemotherapeutic treatments. Owners can expect to see some side effects in their dogs, such as nausea, vomiting, diarrhea, weakness, lethargy, lack of appetite and weight loss.
The prognosis for dogs with any form of cancer is highly variable, depending upon the type of cancer involved, the location of the tumor(s), whether the cancer is malignant and has metastasized, whether the disease was caught early or late in its progress, the commitment and financial status of the owner and the body condition, appetite, activity level and overall health of the affected animal. Despite the severity and scariness of any cancer diagnosis, some dogs with nasal adenocarcinoma can be well-managed with timely detection and aggressive therapy and may live happily for months or even years.