Chronic pain in dogs with bone cancer relieved with new treatment

"Dogs are part of the family and we do everything we can to relieve them of pain and discomfort when they are sick," said Dorothy Cimino Brown, D.V.M., School of Veterinary Medicine, University of Pennsylvania, Philadelphia. "In addition to sharing emotional attachments with our dogs, humans share many of the same ailments our pets suffer when fighting cancer. By studying the positive pain relief this treatment afforded dogs, we are hopeful it may also be effective for humans."

The evolution of bone cancer pain in dogs parallels what occurs in humans, with the frequency and intensity of pain increasing over weeks and months. As the cancer advances, both canine and human patients experience life-altering pain, which greatly affects their daily activities and quality of life. The standard treatment for dogs with late-stage bone cancer can include opioids, steroids, and palliative radiation. All of these treatments can have negative side effects.

The owners of 70 dogs enrolled their pets in this study. Half the dogs received an injection of a neurotoxin, called substance P-saporin (SP-sap), as well as standard care. The other half (i.e., the control group) received standard care without the neurotoxin injection. The average age of the dogs was between 8 and 9 years and their average weight was 90 pounds. Multiple breeds participated in the study, including: Rottweilers, Labrador Retrievers, Golden Retrievers and mixed breeds.

Neurotoxins are historically known for the disease they can cause, such as botulism, according to Dr. Brown. More recently, however, scientists have learned to harness properties of neurotoxins for positive uses. For example, Botox is used to eliminate wrinkles and SP-sap is used to decrease pain. The SP portion of the neurotoxin works by attaching to a pain-sensing nerve and then the "sap" part gets inside the pain-sensing nerve and causes it to die.

Within six weeks of beginning the study, 74 percent (26) of the dogs in the control group needed to be "unblinded" (i.e., their status in the study revealed) and their pain relief regimen adjusted compared to 24 percent of the dogs (eight) in the group that received the injection. This was a statistically significant difference.

Other study results included a 6 percent increase in pain severity scores for dogs in the control group, while the dogs in the SP-sap group had no change in pain severity score. In addition, the dogs in the control group had an 8 percent increase in how pain interferes with their typical activities, while the SP-sap dogs had a 5 percent improvement in this pain impact score. Finally, one dog in the control group responded with improved lameness, while 6 dogs in the SP-sap group became less lame. While these secondary study results were not statistically significant because they were only assessed two weeks after injection, they are promising.

"The overriding goal of this research is to identify breakthroughs in managing chronic pain in both people and dogs by taking advantage of the fact that pets, through the course of their natural lives, develop many of the same medical conditions causing chronic pain that develop in people," said Dr. Brown. "Additionally we can 'measure' this pain in companion animals like we do in people, quantifying severity and impact on routine activities, mobility and sleep."

The positive pain relieving effect that SP-sap had was significant, according to the study. It both provides promising data for canine patients suffering from cancer and encourages further research into the use of SP-sap for chronic pain control in humans.