Cancer pain in cats and dogs
Not all cancers will cause pain to your pet and the amount of pain will likely vary from one animal to another, even for similar
types of tumors. Human studies indicate that 20-50% of human patients experience pain upon cancer diagnosis and up to
90% of human patients experience pain with advanced or terminal cancer. Unfortunately, cancer associated pain has been
largely overlooked by veterinary medicine but it is predicted that pets will experience cancer pain similarly to humans. Many
veterinary hospitals now recognize the importance of treating cancer pain and offer cancer pain management plans tailored
to each pet's unique needs.

In addition to pain caused by the actual tumors, pets will also experience pain associated with cancer treatments such as
surgery, radiation therapy or chemotherapy. Untreated pain decreases quality of life in all patients, and prolongs recovery
from the illness, treatment or injury. It is, therefore, essential that veterinary teams taking care of pets with cancer should
also play a vital role in educating pet owners about recognizing and managing pain in their pets.

It is of extreme importance to make your pet's life as comfortable and painless as possible and to discuss
appropriate cancer pain management for your pet's unique condition with your veterinarian or oncologist.
Veterinarians are ethically obligated to recognize, assess, prevent and provide pain relief to all pets under
their care.

While no formal clinical studies have been conducted to evaluate the effect of specific cancers on pain, the following tumors
are most likely to cause pain.

  •        Bone tumors
  •        Central nervous system tumors (e.g. brain tumors)
  •        Gastrointestinal (e.g. esophagus, stomach, colon, rectum tumors)
  •        Inflammatory breast tumors
  •        Genitourinary tract tumors  (e.g. kidney, bladder tumors)
  •        Prostate tumors
  •        Oral cavity (mouth) tumors
  •        Intranasal (nose) tumors
  •        Invasive skin tumors

Assessment of cancer pain in cats and dogs
Because many cats and dogs may not show obvious signs of cancer pain and also tend to hide pain as a protective
mechanism, identifying the degree of pain and the amount of suffering can be very difficult. The most likely indicators of
pain are changes in the pet's behavior, as summarized below. The pet owners spend the most time with their pets and are,
therefore, the only ones who can really pick up even on the slightest changes in their pet's behavior. The pet owners
should bring up cancer pain management during veterinary visits and should ensure that their veterinarian is fulfilling
his/her ethical obligation if the pet appears to be in pain. However, even if such indicators are absent and it is known that
the same type of tumor causes pain in humans, the pets should be given the benefit of a doubt and be treated for pain as

Likely indicators of pain in cats and dogs
  •        Changes in normal activity level/behavior (e.g. the pet does not play as much, does not want to go for walks)
  •        Change in behavior (e.g. the pet avoids social interaction, hides, shows decrease in energy)
  •        Reluctance to move (e.g. the pet is sitting or lying for prolonged periods of time, shows lameness)
  •        Changes in appetite (e.g. the pet does not want to eat or eats substantially less)
  •        Changes in attitude (e.g. the pet becomes more shy, dull, aggressive or growls when being touched)
  •        Facial expression (e.g. the pet's head hangs low, sad expression, squinted eyes)
  •        Reaction to touch (e.g. the pet cries, growls, or attempts to run away when touched in an affected area)
  •        Respiration (e.g. increased breathing)
  •        Licking/scratching (e.g. the pet may constantly lick/scratch a specific area)
  •        Vocalization (e.g. the pet may whine, grunt, meow, hiss)
  •        Urinary and bowel elimination (e.g. the pets urinate and defecate in inappropriate areas)

Types of pain
Pain is divided into acute and chronic forms, each requiring its own treatment. Acute pain is generally short-lived, lasting
hours to days. Acute pain is usually a result of trauma, treatment therapies (e.g. surgery, radiation therapy), or some
underlying disease. In contrast, chronic pain persists over longer periods of time, lasting weeks or longer. It continues
beyond the expected period of healing and can be more difficult to detect compared to acute pain.

Cancer pain management in cats and dogs
There are two aspects of treating cancer pain in pets. The first aspect is focused on eliminating the source of pain - the
tumor itself. This can be accomplished by a combination of several approaches that can include surgery, chemotherapy
and radiation therapy. The second aspect is focused on treating pain in general and pain associated with the above

Pain management will depend on the type of pain, the species, individual pain tolerance, and the overall health status of the
pet. The best way to manage cancer pain in pets is to prevent it, a term referred to as preemptive pain management. This
strategy anticipates pain ahead of time and administers pain medication before the pet actually experiences pain, thus
ensuring the pet's maximum comfort. Sometimes the veterinarian will have to combine multiple pain therapies in order to
successfully control the pain, a term referred to as multimodal therapy. Cancer pain management typically incorporates the
following drug classes:

  •        Nonopioid analgesics (e.g. nonsteroidal antiinflammatory drugs) - mild to moderate cancer pain
  •        Weaker opioid drugs (e.g. codeine, tramadol) - moderate cancer pain
  •        Strong opioid drugs (e.g. morphine) - moderate to severe cancer pain
  •        Local or regional block using a local anesthetic

Important note: You should never administer any medication to your pet without first consulting your veterinarian to avoid
harming your pet (the type of pain medicine and dose will depend on your pet's size, weight, what other medications your
pet is taking and the specific medical condition).

The World Health Organization has proposed a three-step analgesic ladder for controlling mild, moderate and severe pain
in humans, which is now applied to treating cancer pain in pets. Using this model, mild pain is typically initially treated with
nonopioid drugs. If the pain becomes moderate, the second step would be administration of weaker opioid drugs (e.g.
codeine or tramadol). If that is unable to achieve pain relief and the pain becomes severe, the third step would be
administration of strong opioid drugs (e.g. morphine). For situations where the cancer pain is difficult to control, additional
techniques can be applied such as intrathecal administration of opioids (into the spinal cord), neurostimulation, peripheral
neuroablation (nerve block), and central neuroablation. Nerve blocks refer to the procedure where local anesthetics are
injected into or near nerves to control pain in that region.

Strong opioid drugs
Opioids are heavily utilized in humans with cancer and have become incorporated into pain management plans for cats and
dogs with cancer. These drugs are usually used for treating moderate to severe pain, and can be administered in
combination with other analgesics, including non-steroidal antiinflammatory drugs. The commonly used opioid is morphine,
which can be given either as subcutaneous injection (under the skin), intramuscular injection (into the muscle),
intravenously (into the vein), orally or epidurally. Other opiods include fentanyl (also available as skin patch),
hydromorphone and oxymorphone. Side effects usually become an issue at higher doses and with long-term use, which can
include sedation, constipation, respiratory depression, panting or vomiting.

Depending on your pet's condition, the stage of the disease, and perceived discomfort, the veterinarian will prescribe
appropriate pain relief medication(s) and doses. Pain medications vary in their strength and duration of providing pain
relief, and as the level of pain increases with progression of disease, more powerful and quick acting drugs should be
administered on a regular basis rather than on as-needed basis to maintain the pet's comfort.

Pain resulting from cancer treatments
As mentioned above, pets also experience pain from the cancer diagnostic procedures and treatments such as invasive
biopsies, surgical removal of the tumor, radiation therapy and chemotherapy.

Radiation Therapy
Painful acute side effects of radiation therapy can include inflammation in the mouth, skin, eyes or intestine, which are
typically seen more often with full-course radiation therapy. It is very important to prevent any additional damage to the area
so Elizabethan collars should be used as needed to prevent pets from pawing or licking. Inflammation in the mouth can be
treated with oral rinse solutions (e.g. a weak tea solution, chlorhexidine rinse, or mixture of viscous lidocaine, liquid
diphenhydramine, and magnesium hydroxide). Veterinary radiation oncologists strive to minimize the side effects by using
computerized planning of the radiation treatment along with using modern radiation therapy equipment.

Although chemotherapy is not painful itself, it can result in side effects that are painful. For example, commonly used drug
called doxorubicin can cause colitis (inflammation of the intestine) or drug called vincristine can cause constipation in cats.
Chemotherapy drugs can also cause painful tissue destruction if they leak out during administration.

Additional pain management strategies
In addition to administering pain relieving medication, pain management plan can also include other strategies. Some
commonly used strategies include:

  • General nursing care
  • Comfortable bedding
  • Massages and physical therapy
  • Acupuncture
  • Proper nutrition and dietary supplements

Your veterinarian/oncologist should work closely with you to develop an individualized cancer pain management plan that is
best for your pet's needs, and should routinely follow up with you on the safety and effectiveness of that plan to ensure that
your pet continues to be free of pain and discomfort.

Finding a qualified veterinary oncologist to discuss cancer pain management for your pet
To locate a qualified veterinary oncologist in your area who can discuss with you appropriate cancer pain management for
your pet's condition, please visit the "
Locate a veterinary oncologist" section.  

Other useful online resources about pain management in pets

  • Withrow Stephen J, and David M. Vail. Small Animal Clinical Oncology. St Louis: Saunders Elsevier, 2007
  • Understanding and recognizing cancer pain in cats and dogs by Louis-Philippe de Lorimier, DVM, DACVIM
    (Oncology) and Timothy M. Fan, DVM, PhD, DACVIM (Internal medicine and Oncology)
  • Treating cancer pain in cats and dogs by Louis-Philippe de Lorimier, DVM, DACVIM (Oncology) and Timothy M. Fan,
    DVM, PhD, DACVIM (Internal medicine and Oncology)
Pain Management for Cats
and Dogs with Cancer
© 2007 Pet Cancer Center. ALL RIGHTS RESERVED.
Last updated 2/20/2017

  • Pain is common in pets with cancer and can be detected with careful observation
    of their behavior.
  • Pain negatively impacts the pet's quality of life as well as important physiological
  • Pain can be caused by the tumor itself but also by invasive diagnostic procedures
    (e.g. biopsy) and treatments (e.g. surgery or radiation therapy).
  • Pain management is a key component of the cancer treatment plan for your pet.

  • Eliminating pain in pets with cancer should be a priority but never
    administer any pain medication without first consulting your veterinarian.
Comprehensive guide to cancer diagnosis and treatment in cats and dogs
Pain Management for Cats and Dogs with