Reference
Plain-language definitions of the clinical terms you are most likely to encounter when your pet has been diagnosed with cancer. Browse alphabetically below, or use your browser's find function (Ctrl/⌘ + F) to search for a specific term.
Treatment given after the primary therapy — usually surgery — to reduce the risk of the cancer coming back. For example, a dog might have a mast cell tumour surgically removed, then receive several rounds of chemotherapy as adjuvant therapy to kill any microscopic cancer cells that may have been left behind. Adjuvant therapy is preventive in nature: the visible disease has already been addressed, and the goal is to lower the chance of recurrence or metastasis.
The removal of a sample of tissue from the body so it can be examined under a microscope by a pathologist. A biopsy is usually how a cancer diagnosis is confirmed and how the tumour type and grade are determined. There are several types: an incisional biopsy removes a small piece of a larger mass, an excisional biopsy removes the entire mass, and a punch biopsy uses a small circular blade to take a core sample. Biopsy results are essential for treatment planning — they tell your oncologist exactly what they are dealing with.
When all detectable signs of cancer disappear in response to treatment. This does not necessarily mean the cancer is cured — microscopic disease may still be present — but it is the most favourable short-term response and is usually the primary goal of first-line chemotherapy. Complete remission is strongly associated with longer survival times and gives the best foundation for subsequent maintenance therapy.
Another phrase for complete remission; the two terms are used interchangeably throughout veterinary oncology literature. You may see the abbreviation "CR" in your pet's clinical records or in a protocol summary.
The use of drugs to kill cancer cells or stop them from dividing. In veterinary oncology, chemotherapy is generally much better tolerated than in human medicine — most pets experience only mild side effects, and severe reactions are uncommon. Treatment is typically given as a series of sessions (a protocol) over weeks or months, administered intravenously at the clinic or as oral tablets at home. The specific drugs, doses, and schedule depend on the cancer type and the treatment goals.
A structured research study that evaluates a new treatment, drug, or approach in animals with naturally occurring disease. Veterinary clinical trials can offer access to cutting-edge therapies — sometimes at reduced cost — while contributing to scientific knowledge. Enrolment typically requires meeting specific criteria (tumour type, stage, prior treatment history). Your oncologist or a veterinary teaching hospital can advise whether any open trials are relevant to your pet's diagnosis.
A treatment protocol that uses two or more chemotherapy drugs together, each attacking the cancer through a different mechanism. Combination protocols — such as CHOP for lymphoma — generally achieve higher remission rates and longer survival times than single-agent treatment, because the cancer is less likely to develop resistance when multiple pathways are targeted simultaneously. The trade-off is usually a more complex treatment schedule and closer monitoring for side effects.
A treatment approach where the goal is to eliminate the cancer entirely and achieve a long-term cure. Not all cancers are candidates for curative-intent treatment — it depends on the type, stage, and location of the disease. When cure is realistic, treatment is typically more aggressive (wider surgery, multi-agent chemotherapy, or combined modalities). Curative intent is distinct from remission-focused or palliative approaches, though the boundaries can overlap in practice.
A treatment goal focused on slowing the progression of cancer and keeping it stable for as long as possible, rather than attempting to eliminate it completely. Disease control is a realistic and valuable outcome for many cancers that cannot be cured but can be managed — sometimes for months or years — with ongoing treatment such as metronomic chemotherapy, targeted therapy, or low-dose radiation. The emphasis is on maintaining quality of life while keeping the cancer in check.
A rating that describes how strong the scientific evidence is behind a treatment recommendation. Higher tiers reflect data from large, well-designed prospective clinical trials; lower tiers may draw on smaller retrospective studies, case series, or expert opinion alone. When comparing protocols, the evidence tier helps you understand how much confidence the research community places in the expected outcomes — and where genuine uncertainty still exists.
The standard, most-recommended treatment for a given diagnosis — the option backed by the strongest evidence and the best expected outcomes. Your oncologist will typically start here unless specific factors such as your pet's overall health, concurrent diseases, financial constraints, or drug availability make an alternative more appropriate. Understanding the first-line protocol is usually the best starting point for any treatment conversation.
A quick, minimally invasive diagnostic procedure where a thin needle is inserted into a lump or lymph node to extract a small sample of cells. The sample is placed on a slide and examined under a microscope (cytology). FNA is often the first test performed when a mass is discovered — it can be done during a normal consultation, usually without sedation. It provides preliminary information about whether a lump is likely cancerous, but a full biopsy is often still needed to confirm the tumour type and grade.
A structured quality-of-life assessment tool for pets with serious illness, developed by veterinary palliative care specialist Dr Alice Villalobos. The five Hs and two Ms stand for: Hurt, Hunger, Hydration, Hygiene, Happiness, Mobility, and More good days than bad. Each area is scored, and the totals are tracked over time to guide discussions about whether treatment is maintaining an acceptable quality of life. It is not a replacement for professional veterinary assessment, but it gives families and care teams a shared, concrete vocabulary for conversations that can otherwise be very difficult to have.
A laboratory test that identifies which type of immune cell a tumour originates from, most commonly used to classify lymphoma as B-cell or T-cell. This distinction matters significantly for treatment planning: B-cell lymphoma generally responds better to chemotherapy and carries a more favourable prognosis than T-cell lymphoma. Results from immunophenotyping directly influence which protocol your oncologist recommends and what survival times you might expect.
A class of treatment that works by stimulating or directing the body's own immune system to recognise and attack cancer cells. In veterinary oncology, immunotherapy is a growing field — examples include the canine melanoma vaccine (Oncept), which is used as an adjuvant treatment for oral melanoma after surgery. Immunotherapy typically has a different side-effect profile from chemotherapy and may be used alone or alongside conventional treatments.
Treatment delivered directly into the tumour itself, rather than systemically through the bloodstream. This can include chemotherapy drugs, immunostimulants, or other agents injected into the mass. The advantage is that high concentrations of the drug reach the cancer cells while minimising side effects elsewhere in the body. Intralesional therapy may be used for tumours that are difficult to remove surgically, or as an adjunct to other treatments.
A genetic variant found in certain dog breeds — especially Rough and Smooth Collies, Shetland Sheepdogs, Australian Shepherds, and related herding breeds — that disrupts a protein responsible for pumping certain drugs out of cells. Dogs carrying this mutation can accumulate dangerously high levels of some chemotherapy agents, antiparasitic drugs, and other medications, leading to serious neurological toxicity. Genetic testing is strongly recommended before starting treatment for any at-risk breed.
The point in time by which exactly half the animals in a study had died and half were still alive. It is a statistical summary of a population — not a prediction for your individual pet. Some animals live far beyond the median; others do not reach it. When a protocol summary states "MST 12 months," it means half the dogs in that study were still alive at 12 months. The median is the most commonly reported survival statistic in veterinary oncology, but always worth reading alongside the range of outcomes.
The spread of cancer cells from the original (primary) tumour to other parts of the body, most commonly via the lymphatic system or bloodstream to lymph nodes, lungs, liver, spleen, or bone marrow. The presence and extent of metastasis at the time of diagnosis is one of the most important factors shaping both prognosis and the choice of treatment strategy — local disease and systemic disease are managed very differently.
A low-dose, continuous chemotherapy approach — usually oral tablets given at home daily or near-daily at a fraction of conventional doses. Rather than directly killing tumour cells as high-dose pulse chemotherapy does, it works partly by suppressing angiogenesis (the formation of new blood vessels that tumours depend on to grow) and partly through immune modulation. It is commonly used as a maintenance strategy after remission, for palliative control of slow-growing tumours, or when conventional intensive chemotherapy is not feasible.
A treatment approach that combines two or more different types of therapy — for example, surgery followed by chemotherapy, or radiation alongside a tyrosine kinase inhibitor. Many cancers respond best when multiple strategies are used together, since each targets the disease through a different mechanism. Understanding which modalities are recommended (and why) is central to evaluating treatment plans.
A veterinarian who has completed several additional years of specialist training in cancer medicine, typically leading to board certification as a Diplomate of the American College of Veterinary Internal Medicine — Oncology (DACVIM Oncology) or equivalent international qualification. Veterinary oncologists see cancer cases every day, know the latest treatment protocols, and can offer options that a general practitioner may not be aware of. A referral to an oncologist does not mean your regular vet has failed — it is the system working as it should.
Treatment focused on relieving symptoms, maintaining quality of life, and minimising suffering — rather than attempting to eliminate the cancer. Palliative care is an active, compassionate strategy, not simply "doing nothing," and may include pain management, anti-nausea medication, nutritional support, or low-dose chemotherapy. It can be the primary approach from the outset or used alongside curative-intent treatment. The goal is that your pet has the best possible life for however long that is.
A medical assessment of the likely course and outcome of a disease — in practical terms, what you can expect to happen. Prognosis is shaped by many factors: the cancer type, grade, stage, your pet's overall health, and how the cancer responds to treatment. Oncologists often describe prognosis in ranges rather than certainties, because individual animals can vary widely. Asking about prognosis is a natural and important part of the conversation — there are no wrong questions here.
When treatment causes a tumour to shrink measurably — typically defined as a reduction of 30% or more in tumour size — but does not eliminate all detectable cancer. Partial remission is a positive response and can be associated with meaningful improvements in quality of life and comfort, even when complete remission is not achieved. You may see it abbreviated as "PR" in clinical notes.
When the cancer continues to grow or spread despite treatment, or when it returns after a period of remission. Progressive disease typically prompts a reassessment of the treatment plan and may lead to a switch to a rescue or second-line protocol. It is often abbreviated as "PD" in clinical records.
A standardised treatment plan that specifies which drugs are used, at what doses, by which route (intravenous, oral, subcutaneous), and on what schedule. Protocols are typically named by acronyms reflecting the drugs they contain — for example, CHOP uses Cyclophosphamide, Hydroxydoxorubicin (doxorubicin), Oncovin (vincristine), and Prednisolone. Following a named protocol makes outcomes reproducible and comparable across different clinics and published studies, which is why your oncologist may refer to it by its acronym.
A holistic assessment of your pet's day-to-day wellbeing during and after treatment — encompassing comfort, appetite, mobility, happiness, and freedom from pain or distress. Quality of life is increasingly central to veterinary oncology: the goal is not simply to extend life but to ensure that the time your pet has is good time. Many oncologists will discuss QOL explicitly at the first appointment, and structured scoring tools like the HHHHHMM scale can help you and your vet track how your pet is doing over time.
The use of high-energy radiation beams to damage the DNA of cancer cells and prevent them from growing. In veterinary oncology there are two broad approaches: definitive radiation uses many small daily doses over several weeks with the aim of eliminating the tumour while sparing surrounding tissue; palliative radiation uses fewer, larger doses over a shorter period to reduce pain and shrink a tumour enough to improve quality of life, without aiming for cure. Radiation requires general anaesthesia for each session — not because it is painful, but because the patient must remain perfectly still.
The return of cancer after a period of remission or after initial treatment appeared to have controlled the disease. Relapse can occur at the original site (local recurrence) or in other parts of the body (distant recurrence or metastasis). It does not mean that treatment failed — many cancers go through cycles of response and relapse, and second-line or rescue protocols may achieve further remissions. Your oncologist will have anticipated this possibility and will have options to discuss.
When treatment is aimed at achieving remission — the disappearance or significant reduction of detectable cancer — rather than outright cure. This is the most common treatment intent for cancers like lymphoma, where cure is rare but remission periods of months to years are achievable and can be accompanied by excellent quality of life. Remission-focused treatment acknowledges that the cancer will likely return eventually, but the time in remission is often very good time for your pet.
A treatment protocol used when a first-line or second-line regimen has stopped working, or when the cancer has relapsed after a remission period. The goal may be to re-achieve remission, slow progression, or maintain quality of life for as long as possible. Response rates to rescue protocols are generally lower than to first-line treatment, but some pets do achieve meaningful additional remission periods.
The surgical removal of a tumour, which may be the primary treatment or part of a multimodal approach. In oncological surgery, the goal is not just to remove the visible mass but to take it out with clean margins — a border of normal tissue around the tumour to reduce the risk of leaving cancer cells behind. Some surgeries are curative on their own (particularly for low-grade, well-localised tumours), while others are followed by adjuvant chemotherapy or radiation. Debulking surgery, where only part of the tumour is removed to reduce its size, may be used when complete removal is not feasible.
Any treatment used after the initial (first-line) regimen has been completed, failed, or become no longer appropriate. Second-line options may include different drug combinations, targeted therapies, radiation, or a palliative approach. The term refers to sequence in the treatment timeline rather than the intent — rescue protocols are a specific type of second-line therapy aimed at achieving a new remission after relapse.
When the cancer neither shrinks enough to qualify as a remission nor grows enough to qualify as progressive disease — it is holding steady. Stable disease can be a meaningful and acceptable outcome for slow-growing cancers, and may be maintained over time with strategies such as metronomic chemotherapy or targeted therapy. It is sometimes abbreviated as "SD."
The process of determining how far a cancer has spread through the body at the time of diagnosis. Staging typically involves a combination of physical examination, imaging (radiographs, ultrasound, CT scan), lymph node sampling, and blood and bone marrow testing. Cancer is assigned a Stage — usually I through V — with higher numbers indicating more widespread disease. Stage directly shapes both prognosis and treatment recommendations, and completing staging before committing to a treatment plan is generally worthwhile.
A further refinement within a staging category that describes the animal's clinical condition at diagnosis. In veterinary lymphoma, substage "a" means the animal appears clinically well (no overt signs of systemic illness), while substage "b" means the animal is showing signs such as weight loss, lethargy, or reduced appetite. Substage often influences prognosis as much as the stage number itself — a dog at Stage III substage a will typically have a better prognosis than one at Stage III substage b.
A treatment that acts against specific molecular targets — such as a mutated protein or overactive receptor — on or inside cancer cells, rather than using broadly cytotoxic agents like standard chemotherapy. Because targeted therapies are more selective, they can sometimes cause fewer side effects, though this varies considerably by drug and patient. In veterinary oncology the best-established targeted therapies are tyrosine kinase inhibitors used for mast cell tumours.
A pathologist's assessment of how abnormal cancer cells appear under the microscope, and how quickly the tumour is likely to grow and spread. Grade is typically described as Low, Intermediate, or High (or Grade I, II, III). High-grade tumours tend to be more biologically aggressive, spread more readily, and often require more intensive treatment. Grade is distinct from stage: stage describes where the cancer has spread, whereas grade describes the behaviour of the cells themselves.
A class of targeted therapy drugs that block enzymes called tyrosine kinases, which cancer cells often depend on for uncontrolled growth and survival signals. In veterinary oncology, TKIs such as toceranib phosphate (Palladia) and masitinib are most commonly prescribed for mast cell tumours and certain other cancers. They are typically given as daily oral tablets at home, and they work through a fundamentally different mechanism than conventional chemotherapy — which also means their side-effect profile differs.
A deliberate, monitored decision to observe a tumour closely — with scheduled re-examinations and possibly repeat imaging — without initiating active treatment immediately. This may be appropriate for very slow-growing or low-grade tumours, for animals whose overall health makes treatment high-risk, or when the anticipated benefits of treatment are not yet likely to outweigh the burdens. Watchful waiting is an active strategy requiring regular reassessment, not simply doing nothing.
When a surgeon removes a tumour with a generous border of normal-appearing tissue on all sides — not just the visible tumour mass — to reduce the risk of leaving cancer cells behind (called "positive" or "dirty" margins). The width of margin required depends on the tumour type and grade. Achieving clean wide margins at the first surgery generally provides the best chance of local tumour control; re-excision of the same site is technically more difficult, and microscopic disease left behind increases the risk of local recurrence.