November is Pet Cancer Awareness Month, a subject we return to each year at Boundary Bay Veterinary Specialty Hospital (BBVSH). Our board-certified veterinary oncologists diagnose and treat pets with cancer every day, making this an important opportunity to help pet owners better understand a disease that can be both complex and frightening.
This year, we’re taking a closer look at what cancer is actually doing inside your pet’s body. Understanding some of the biology behind cancer can help make sense of why cancers behave differently, why veterinarians recommend certain tests, and why there is no single treatment plan that works for every patient.
As Dr. Sarah Charney, DVM, DACVIM, DACVR , board-certified veterinary medical and radiation oncologist and co-owner of BBVSH, explains, understanding the cancer process is an important part of understanding the choices that come next. For families facing a cancer diagnosis, that knowledge can help replace some of the fear and uncertainty with information, options and hope.
What Is Cancer?
Your pet’s body is made up of trillions of cells. Normally, those cells follow carefully regulated processes controlling when they grow, divide and die. Cancer develops when genetic changes disrupt those controls, allowing abnormal cells to survive and reproduce when they normally would not.
This process is known as malignant transformation. As cancer develops, cells can acquire characteristics that allow them to keep dividing, resist apoptosis — the programmed cell death that normally removes damaged or unnecessary cells — and, in some cancers, invade surrounding tissues.
Over time, abnormal cells may accumulate and form a tumour. Benign tumours do not metastasize, or spread to distant parts of the body, although they can still cause significant problems because of their size, location or effects on surrounding structures. Malignant tumours — cancers — can invade nearby tissues and may metastasize elsewhere in the body.
Cancer isn’t one disease. There are many different cancers arising from different cell types, with different biological behaviours. That’s one reason a diagnosis of “cancer” is only the beginning of the conversation.
Why Do Pets Develop Cancer?
There usually isn’t one simple answer. Cancer develops through genetic changes within cells, and a combination of inherited and acquired factors may contribute to those changes.
Genetics can influence cancer risk, which is one reason certain cancers occur more frequently in some breeds. Age is also an important factor: as pets get older, cells have had more time to accumulate genetic changes. Environmental exposures, some viruses and other biological factors may contribute to particular cancers as well.
For most individual pets, however, it isn’t possible to point to one event and say, “that’s what caused the cancer.” For families facing a diagnosis, the more useful questions become: What type of cancer does my pet have? How is it behaving? Has it spread? And what can we do about it?
How Does Cancer Grow and Spread?
For a tumour to continue growing, cancer cells need access to oxygen and nutrients. Some tumours stimulate the formation of new blood vessels through a process called angiogenesis, creating a blood supply that helps support continued growth.
Some cancers remain confined to the place where they began. Others acquire the ability to invade nearby tissues and metastasize — spread from the original tumour to other areas of the body. Cancer cells may enter blood vessels or the lymphatic system, travel to another location and establish new tumours there.
Different cancers have different tendencies and patterns of spread. That biology is one reason your oncologist needs to know more than simply whether cancer is present.
It also helps explain staging. Staging evaluates the extent of cancer in the body and, depending on the cancer, may involve examining or sampling lymph nodes, bloodwork, X-rays, ultrasound, CT or other diagnostic imaging. The information helps the Oncology team understand the extent of disease and determine which treatment options are appropriate.
How Do Veterinarians Know What Kind of Cancer It Is?
A lump or abnormality doesn’t tell us everything about the cells inside it. Your family veterinarian may begin with a physical examination, bloodwork, imaging or a fine needle aspirate, which uses a small needle to collect cells for cytology — examination of individual cells under a microscope.
In other cases, a biopsy is needed to collect a piece of tissue for histopathology, which allows a veterinary pathologist to examine the cells as well as how they are arranged within the tissue. Histopathology can help identify the tumour type and, for some cancers, provide a grade — information about how abnormal the cancer cells appear and how aggressively the tumour may be expected to behave.
Grade and stage aren’t the same thing. Grade describes characteristics of the tumour itself; stage describes the extent of disease in the patient. Both can be important when an oncologist is considering prognosis and treatment.
For some cancers, additional molecular or genetic testing can further characterize the disease. We saw how important this can be with Lucy the Wonderdog, a BBVSH patient who developed more than one type of cancer. Molecular diagnostics helped provide more precise information about her cancers and guide treatment decisions over several years.
Read Lucy the Wonderdog’s story and learn how molecular diagnostics are changing cancer care for pets.
At BBVSH, our board-certified oncologists also work with our Surgery, Internal Medicine and Diagnostic Imaging teams onsite when a patient’s diagnosis or treatment involves more than one area of specialty medicine.
Why Isn’t Every Cancer Treated the Same Way?
Because the biology is different.
For a localized tumour, surgery may offer an opportunity to remove the cancer. Chemotherapy uses medications to kill cancer cells or interfere with their ability to grow and divide and is often important for cancers that are systemic — affecting the body more broadly — or have a significant risk of metastasis. Radiation therapy delivers targeted ionizing radiation that damages cancer cells and may be used alone or in combination with surgery or chemotherapy.
Some cancers may also be treated with targeted therapies, which act on particular molecular features or pathways involved in cancer growth, or immunotherapy, which uses the immune system to recognize or respond to cancer.
Palliative care has a different goal: controlling pain and other symptoms and maintaining quality of life when cure or long-term control isn’t the objective.
There is no single “right” cancer treatment. The plan depends on the tumour type, grade and stage, its expected biological behaviour, your pet’s overall health, the potential benefits and adverse effects of treatment, and your family’s goals.
Is Chemotherapy Different for Pets?
This is one of the questions veterinary oncologists hear frequently. Many people understandably associate chemotherapy with the difficult side effects experienced by friends or family members undergoing human cancer treatment, but veterinary oncology approaches treatment with a strong emphasis on quality of life.
Side effects can occur, including nausea and decreased appetite, and patients are monitored so treatment can be adjusted when needed. In general, pets tend to tolerate chemotherapy side effects better than people. The goal isn’t simply more time — it is more good days.
There are also many misconceptions about what cancer treatment will mean for a pet and their family, from concerns about chemotherapy side effects to assumptions about prognosis.
Related: Read Dr. Charney’s answers to 10 common misconceptions about pet cancer treatment
What Signs of Cancer Should Pet Owners Watch For?
Cancer can affect almost any part of the body, so there isn’t one set of symptoms. A new or changing lump, unexplained weight loss, decreased appetite, persistent sores or swelling, unexplained bleeding, difficulty breathing or swallowing, recurring vomiting or diarrhea, persistent coughing, pain or a noticeable decrease in normal activity are all changes worth discussing with your family veterinarian.
These signs don’t necessarily mean your pet has cancer. Many can occur with other medical conditions, but a persistent or unexplained change is worth investigating.
Related: Read the Top 10 Warning Signs of Cancer in Pets
What Happens If My Pet Is Diagnosed With Cancer?
A cancer diagnosis can feel like the moment everything changes. But the word cancer alone doesn’t tell you what happens next. The next step is understanding your pet’s particular cancer: where it started, what type it is, its grade and stage when those measures apply, how it is expected to behave, and what treatment options are available.
Your family veterinarian remains an important part of that process. If cancer is suspected or confirmed, they may recommend referral to a board-certified veterinary oncologist for further diagnostics and treatment planning. At BBVSH Surrey, our board-certified Oncology team works with families to explain the cancer process, discuss available options and develop an individualized plan with quality of life at its centre.
For some pets, that means surgery, chemotherapy, radiation or a combination of treatments. For others, it may mean managing symptoms and prioritizing comfort. Families also often have questions about caring for a pet during cancer treatment, including what role nutrition may play.
Related: Nutrition and Cancer — What Should You Feed a Pet With Cancer
Understanding the biology doesn’t make a cancer diagnosis easy. But it can replace some of the uncertainty with information — and help families make decisions based on their pet, their cancer and what matters most to them.
Understanding Cancer in Pets: Frequently Asked Questions
What is cancer in dogs and cats?
Cancer develops when genetic changes disrupt the normal controls that tell cells when to grow, divide and die. These abnormal cells may continue reproducing, form a tumour, invade surrounding tissues and, in some cancers, spread to other parts of the body.
What causes cancer in pets?
There usually isn’t one single cause. Cancer develops through genetic changes within cells, and inherited genetics, age, environmental exposures, some viruses and other biological factors can contribute. For most individual pets, it isn’t possible to identify one specific event that caused their cancer.
What is the difference between a benign and malignant tumour?
A benign tumour does not metastasize, or spread to distant parts of the body, although it can still cause problems because of its size or location. A malignant tumour is cancer: its cells can invade surrounding tissues and may have the ability to spread elsewhere in the body.
How does cancer spread in dogs and cats?
The spread of cancer is called metastasis. Cancer cells can invade surrounding tissues and may enter the bloodstream or lymphatic system, travel to other areas of the body and establish new tumours. Different types of cancer have different tendencies and patterns of metastasis.
What is cancer staging in pets?
Cancer staging evaluates the extent of cancer in a pet’s body, including whether it has spread beyond its original location. Depending on the type of cancer, staging may involve bloodwork, lymph node or tissue sampling, X-rays, ultrasound, CT or other diagnostic imaging. Staging helps a veterinary oncologist assess the disease and consider appropriate treatment options.
What is the difference between cancer grade and cancer stage?
Grade describes characteristics of the tumour itself, including how abnormal the cancer cells appear and, for some cancers, how aggressively the tumour may be expected to behave. Stage describes the extent of cancer within the patient’s body. Both can provide important information for treatment planning and prognosis.
How do veterinarians diagnose cancer in pets?
Diagnosis may involve a physical examination, bloodwork, diagnostic imaging and sampling abnormal cells or tissue. A fine needle aspirate collects cells for cytology, while a biopsy collects tissue for histopathology. Some cancers may require additional molecular or genetic testing to more precisely characterize the disease.
Why might a pet with cancer need molecular diagnostics?
Molecular and other specialized diagnostic tests can provide information beyond simply identifying that cancer is present. In some cases, they can help characterize a particular cancer more precisely and provide information that helps a veterinary oncologist make treatment decisions.
Why aren’t all cancers in pets treated the same way?
Cancer isn’t one disease. Different cancers arise from different cells and can have very different biological behaviours. Treatment may depend on the tumour type, grade and stage, risk of metastasis, the pet’s overall health, expected benefits and adverse effects of treatment, and the family’s goals. Options can include surgery, chemotherapy, radiation therapy, targeted therapies, immunotherapy or palliative care.
Do dogs and cats tolerate chemotherapy differently than people?
Pets generally tolerate chemotherapy side effects better than people, although adverse effects such as nausea and decreased appetite can occur. In veterinary oncology, treatment is planned and monitored with a strong emphasis on maintaining the pet’s quality of life, and treatment can be adjusted when needed.
What are the warning signs of cancer in pets?
Possible signs include a new or changing lump, unexplained weight loss, decreased appetite, persistent sores or swelling, unexplained bleeding, difficulty breathing or swallowing, recurring vomiting or diarrhea, persistent coughing, pain or decreased activity. These signs can also occur with many non-cancerous conditions, so persistent or unexplained changes should be assessed by a veterinarian.
Related: Read the Top 10 Warning Signs of Cancer in Pets
When should my pet see a veterinary oncologist?
Your family veterinarian may recommend referral to a board-certified veterinary oncologist when cancer is suspected or diagnosed and specialized diagnostics, staging or treatment planning may be helpful. A veterinary oncologist can help determine the cancer type and behaviour, discuss available treatment and palliative-care options, and develop an individualized plan based on the pet and family’s goals.
