By Don Jergler,
from Veterinary Practice News.
"Find out the latest treatments.
Nasal tumors are rare in companion animals, but experts are reporting more cases of the potentially deadly condition. And, rather than being random outbreaks, they may be a function of greater life spans.
"We are seeing more cancer in animals, and some of that probably is related to better care and animals living longer," said Nicole Northrup, DVM, Dipl. ACVIM, an oncologist and associate professor at the University of Georgia College of Veterinary Medicine.
Ironically, pet owners may have something to do with the anecdotal increase in the incidence of nasal cancer. More clients are willing to pay extra for diagnostics such as CT scans and biopsies to catch cancerous tumors in time to begin treatment, experts say.
Just how many more cases experts have come across is not an exact science, said Philip J. Bergman, DVM, MS, Ph.D., Dipl. ACVIM. In fact, Dr. Bergman, director of clinical studies for the VCA hospital chain, said more tumors of all types are being discovered as the pet population lives longer.
"As we get better with preventive medicine and continue to be better doctors and diagnosticians, the chance for rates going up in general is possible," Bergman said. "That would be tumors across the board."
These improvements and advancements mean more pets are brought in by pet owners encouraged by mroe and better treatment options, said Michael W. Nolan, DVM, Ph.D., Dipl. ACVR, an assistant professor of radiation oncology and biology at the North Carolina State University College of Veterinary Medicine.
"There is no data to suggest that canine nasal cancer is becoming any more prevalent than in the past," Dr. Nolan said. "However, as oncology specialists, we do see more of these cases referred for treatment. I think that is because there are some new treatment options that make nasal cancer management far more tolerable - fewer side effects - and in some cases much more convenient than was possible with conventional treatment options."
Improved treatments largely focus on reducing the damage to surrounding healthy tissue.
Michele A. Steffey, DVM, Dipl. ACVS, an assistant professor in surgical and radiological sciences at the University of California, Davis, School of Veterinary Medicine, is known for her work on interventional oncology techniques and minimally invasive approaches to treating cancer. She is developing a nasal cancer treatment that involves freezing the tumor. Called transnare cryoablation, the goal is to slow the progression and improve the pet's quality of life.
The procedure is minimally invasive, involves no surgical incisions and is done under general anesthesia with CT guidance. The procedure utilizes needle-shaped cryoprobes and medical gasses for a controlled deep freeze to kill the tumor. It is similar to procedures done in human medicine to treat kidney and prostate tumors.
Dr. Steffey for now considers radiation the "gold standard" of treatment.
"Generally, radiation is considered the treatment of choice as a balance between efficacy/positive impacts to clinical signs and survival times versus possible risks and side effects to the patient," Steffey said. "But radiation doesn't generally effect a cure for nasal tumors, so we are continuing to look for ways to improve treatment options and patient outcomes."
A dog with a nasal tumor is seen in a cross-section view. The top image shows the high-dose distribution typically seen with conventional radiation therapy. In the orange area, both eyes (contoured by blue circles) are receiving a high dose of radiation.
Intensity-modulated radiation therapy and stereotactic radiation therapy are the next steps being taken. These therapies provide a more targeted treatment of tumors and prevent excess radiation in critical areas like the face, mouth, eye and brain.
Not only is surrounding tissue protected with the new targeted therapies, but tumors require fewer treatments, Georgia's Northrup said.
Traditional radiation might require 10 to 20 sessions, but stereotactic radiation may involve only three, she said.
"That means less anesthesia, less time in the hospital," Northrup added.
Intensity-modulated radiation therapy, or IMRT, is more readily available, and some clinics use human facilities to treat pets as veterinary practices slowly acquire the equipment, she said.
The availability of the newer modalities isn't growing fast enough for Bergman's taste. Veterinary radiation treatments sometimes are performed using older equipment purchased from human medicine, he noted.
"Most of the time when radiation is done in veterinary medicine, it often is done with what I like to call these 'hand-me-down machines' coming out of human facilities," Bergman said.
Many of the machines are five to 10 years old and were purchased at a discount. The deals might be good, he said, but the trade-off is the inability to confine treatments to a very specific area.
"Nasal tumors is where we welcome that type of precision," Bergman said.
This traditional external beam radiation therapy, as it's called, inadvertently treats normal tissue around a tumor. For nasal cancer, this is a particular concern.
"Unfortunately, that is a site that is sensitive to radiation therapy, so there are a lot of side effects to that," Bergman said.
One potential side effect of radiation is mucositis, the painful inflammation and ulceration of the mucous membranes, Bergman said. It can lead to pain, loss of appetite and infection.
Mucositis is among many potential side effects that has Bergman excited about newer radiation modalities.
"We see remarkably fewer side effects in those patients," he said. "That, to me, is one of the bigger advances we've had, especially for nasal tumors."
North Carolina State's Nolan said the advantages of these therapies, particularly stereo-tactic radiation therapy, or SRT - an even more focused form of treatment than IMRT - are taht they enable a full course of therapy to be give in fewer sessions. And there are few side effects.
"SRT allows high doses of radiation to be given very quickly," Nolan said. "In our clinic, SRT condenses full-course radiation therapy down to three daily treatments. Short-term side effects are minimal, and SRT appears to be as effective as conventional RT."
In a study published in 2010 in Canadian Veterinary Journal, 12 dogs with nasal tumors were treated with IMRT. Clinical signs were resolved in eight dogs during radiation therapy, and the median overall survival time was 446 days. The one- and two-year survival rates were 50 and 25 percent, respectively.
This image shows an intensity-modulated radiation therapy plan for the same dog. Most of the eyes don't receive a high dose of radiation.
What About Surgery?
Asked about the surgical option to treat nasal cancer, UC Davis' Steffey noted that nasal tumors can be caused by a variety of underlying cancers, including lymphoma, carcinomas or sarcomas.
"Most of those tumors are not very sensitive to chemotherapy - the notable exception being lymphoma, and for that type of tumor, chemo generally is recommended," Steffey said. "Historically we avoid traditional surgery for nasal tumors because the surgical approach is very invasive, and there are risks of life-treatening hemorrhage associated with surgery in this area.
"In the majority of cases we can't effect a cure with surgery alone because of anatomical limitations of the nose and the extent of the disease at diagnosis, so the overall balance of risk to benefit doesn't often justify surgery. Of course, there are exceptions to every rule, but in general that covers most cases."
Northrup called surgery "controversial" because that option in dogs often didn't seem to improve survivability and surgery is "not routine at this point."
"I would say the standard of care is radiation therapy," Northrup added.
Bergman also weighed in on the surgical option.
"Typically most tumors are located deep inside the nose, therefore surgery is not very beneficial," Bergman said.
He added that most nasal tumors are in the turbinates, the curled bone shelf that protrudes into the breathing passage of the nose.
Some practitioners are trying therapies using NSAIDs or Palladia, from Zoetis Inc., which typically is indicated for the treatment of mast cell tumors but is thought to have some effectiveness in treating nasal tumors, he said.
"We're still learning how much of a difference that [does] or doesn't make," Bergman said.
He often prescribes Palladia to pets of clients who cannot afford radiation therapy or who live so far away that radiation treatment may not make logistical sense.
Nasal Tumors in Cats?
Feline nasal tumors aren't unheard of, but they are a different animal all together compared with the condition in dogs.
Northrup said that what is seen in cats is mostly lymphoma. With dogs it's carcinoma.
The upshot of lymphoma in the noses of cats is it's typically in a solitary site, she added.
Studies have shown that cats living with cigarette smokers are more predisposed to certain types of cancer, including nasal cancer, Bergman said.
One study Bergman pointed to has been around for a while. A 2002 study published in the American Journal of Epidemiology showed that cats with any history or household exposure to tobacco smoke had a twofold increase in the risk of malignant lymphoma.
"Risk increased with both duration and quantity of exposure, with evidence of a linear trend" the authors stated."
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