Pain Management for Cancer Patients


One of the biggest concerns you may have concerning your pet’s diagnosis of cancer is whether or not he or she is in pain. Pain associated with cancer in animals is fairly common although we may not always be able to detect it. Whether or not your pet is feeling pain depends on the type and location of the cancer as well as the therapy used to treat the cancer.

Treating pain in our animals with cancer is important not only from a humane perspective but also because chronic, untreated pain can negatively impact important physiologic functions such as wound healing, immunologic defenses, and even the ability to respond to pain treatment. The earlier pain is treated, the easier it is to manage over time and the better quality of life experienced by our animal companions.


Some obvious signs of pain include limping, crying out, guarding the area of the body, reluctance to move, decreased or loss of appetite, change in behavior (becoming more aggressive or more submissive), sleeping more, lack of interest in normal activities, and for cats, decreased grooming and change in litter box habits.

There may be other more subtle signs, so it is important for you as your pet’s voice to express your concern to your oncologist or veterinarian if you feel your pet is experiencing pain.

Examples of Tumors That Cause Pain in Veterinary Patients

Tumor Type

Expected Severity of Pain


Primary Bone Sarcoma

Moderate to Severe

Osteosarcoma is the most common (80%), followed by other sarcomas. Most are painful and cause a combination of lytic (destruction of bone) and blastic changes

Joint Tumors

Moderate to Severe

Stretching of the capsule and invasion into bone by primary joint tumors (synovial cell sarcoma, histiocytic sarcoma) or rumors invading around joints (oral tumor invading temporomandibular joint) can be very painful

Metastatic Bone Cancer

Moderate to Severe

Primary carcinomas are from the mammary gland, prostate, anal sac apocrine glands, lungs (cats), and bladder transitional cells. A common site is the spine (especially the lumbar region), but long bones can also be affected. In cats, digit metastasis from pulmonary carcinoma is well-reported. Most metastatic bone tumors are painful, and they most commonly are lytic (destruction of the bone)

Multiple Myeloma

Moderate to Severe

A common feature is osteolytic lesions (spine, long bones), with a risk of pathologic fractures. They can also compress nervous tissue (spinal cord)

Oral Tumors

Mild to Severe

Many will cause bone destruction and soft tissue inflammation. The most common oral tumors in dogs are melanoma, squamous cell carcinoma, and fibrosarcoma. In cats, squamous cell carcinoma is the most common (70%)

Nasal Tumors

Mild to Severe

Nasal tumors can cause considerable destruction and invasion of surrounding tissues, leading to pain

Urinary Tumors

Mild to Severe

Pain can be from invasion of tissues and inflammation, spasms, urinary obstruction, or renal capsule stretching.

Prostate Tumors

Mild to Severe

Pain is from similar causes as those in urinary tumors

Vaginal Tumors

Moderate to Severe

Pain if from similar causes as those in urinary tumors

Mammary Gland

None to Severe

Inflammatory carcinoma is the most painful, associated with pain in nearly 100% of cases. Lymphatic obstruction can be painful


Moderate to Severe

The carcinomatosis is from various tumors (carcinomas, mesothelioma, sarcomas), and diffuse body cavity pain occurs secondary to serosal involvement. Pleural pain can be severe.

Mast Cell Tumors

None to Severe

Mast cell tumors are especially painful when degranulation and peritumor inflammation are present. Some ulcerated and inflamed carcinomas can be painful.

Pancreatic Carcinoma

Moderate to Severe

Pancreatic carcinomas are very painful in people; probably an important component in veterinary pancreatic carcinoma patients as well

Liver & Splenic Tumors

None to Moderate

Stretching the capsule, from primary or metastatic neoplasia can cause considerable visceral pain

Orbital Tumors

Moderate to Severe

Tumors can be primary orbital tumors or secondary to invasion by oral or sinonasal tumors; can cause pain upon opening the mouth

Central Nervous Tumors

Moderate to Severe

The tumors can be primary CNS tumors, or disseminated neoplasia (lymphoma, carcinomas, melanoma, and sarcomas) and can involve the meninges and nerves, or sinonasal tumors can involve the cranial vault. Headaches are common in people with brain tumors

Ear Tumors

Mild to Severe

Ear canal tumors can be painful, especially when secondary infection is present. Middle ear tumors, although uncommon, can be very painful, with bone destruction and pain upon opening the mouth

Brachial Plexus Tumors

Moderate to Severe

These tumors are uncommon but are most often very painful from direct neuropathic and neurogenic pain

Above table is from Understanding and Recognizing Cancer Pain in Dogs and Cats; May 1, 2005: By Lousi-Phillippe de Lormier DVM DACVIM (oncology) and Timothy M. Fan, DVM Ph.D. DACVIM (internal medicine, oncology)


The first step in treating cancer pain is treating the cancer. If the therapies are not recommended in your pet’s particular case or you have decided not to pursue these treatments then the next step is to start pain medications.

There are many different types of pain medications or analgesics, as they are sometimes known. Most of these medications are safe and effective with some negative side effects. They include: non-steroidal anti-inflammatories (NSAIDs), opioids, corticosteroids, anticonvulsants (used for their analgesic properties), antidepressants, NMDA receptor blockers, and local anesthetics.

The most common side effects of these medications are decreased appetite, vomiting, diarrhea, and sedation. Your oncologist or veterinarian may periodically run blood work to monitor kidney and liver values. Any time you feel your pet may be experiencing a side effect from any medication you should call your veterinarian.


It is important to keep in mind that individual animals respond differently to pain medication. This means that frequent reassessment is key to good pain control. Your doctor will ask you regularly about how you feel your pet is responding to the pain medications. We often start with lower doses and fewer types of pain medications and increase them over time as needed.

Regardless of your pet’s diagnosis or treatment plan, the main goal is to improve or maintain a good quality of life. Many people worry that they will not be able to tell when their pet is feeling pain. We will do our best to help guide you and determine the best pain management plan for your pet’s particular situation.