Cancer is one of the most common serious conditions diagnosed in dogs and cats, and while that is sobering, the more useful thing to know is that early detection genuinely changes outcomes. The cancers seen most often include lymphoma, mast cell tumors, osteosarcoma, and mammary tumors in dogs, plus lymphoma and squamous cell carcinoma in cats, each behaving differently, responding to different treatments, and carrying a different prognosis depending on how far it has progressed. Early signs are often subtle: a lump that seems minor, gradual weight loss, a shift in energy, or a slow-healing sore. Cats are especially good at masking discomfort, which means routine exams and a willingness to investigate the non-obvious are the most reliable tools available.

At Arcata Animal Hospital, our diagnostic capabilities include digital radiography, abdominal and cardiac ultrasound, in-house laboratory testing, and cytology with board-certified pathologist review, so we can evaluate a suspicious lump, lymph node, or internal change thoroughly rather than waiting on outside results. We use gentle, anxiety-reducing techniques throughout every appointment to keep the process as low-stress as possible for your pet. If you have noticed something that has been sitting in the back of your mind, call us and we will take a look together.

Cancer in Dogs and Cats at a Glance

  • Cancer is largely a disease of aging: pets get it more now because they live longer with better preventive care, not because something is newly wrong.
  • Many pet cancers are highly treatable when caught early: a mast cell tumor at 1 cm is a very different conversation than one at 6 cm.
  • Subtle changes deserve a same-week visit: a new lump, persistent sore, weight loss, or behavioral shift is enough, and you do not need a working theory to call.
  • Cytology and biopsy answer the question: watching a lump and guessing rarely does.

What Is Cancer in Pets?

Cancer in pets, like in people, is abnormal cell growth that invades nearby tissue or spreads through the body. The reason we see more of it now than thirty years ago is not that something has changed about cancer; pets are simply living long enough to get it. Better nutrition, year-round prevention, and earlier disease management have extended life expectancy, and the cancers that show up most often are cancers of aging.

Not all cancers are fatal. Some are slow-growing local nuisances, while others are aggressive and need same-week intervention. Many are highly treatable when caught early, which is the whole point of preventive healthcare and regular wellness visits.

What Are the Common Types of Cancer in Dogs and Cats?

There are dozens of cancer types in pets, but a handful account for most of what we see and are worth knowing the warning signs for.

Cancer Hallmark sign Most affected
Lymphoma Swollen lymph nodes in dogs; GI signs in cats Dogs and cats
Mast cell tumor Skin lump that changes size Dogs
Mammary tumor Swelling along the mammary chain Intact or late-spayed females
Osteosarcoma Persistent limb lameness Large and giant dogs
Squamous cell carcinoma Non-healing crusty sore White cats, on ears and nose
Hemangiosarcoma Sudden collapse, pale gums Senior dogs, spleen or heart

Oral Tumors

Oral tumors are among the most common cancers in both dogs and cats, ranging from benign growths to aggressive malignancies, and they can look identical to a dental problem such as a swollen gum, a loose tooth, bad breath, or a small mass behind the back molars. Many are caught during dental cleanings, one reason we examine the mouth carefully at every routine visit and recommend regular professional dental cleanings.

Melanoma

Melanoma develops from pigment-producing cells and most often appears inside the mouth, on the lips, around the eyes, or at the nail beds. Skin melanomas are usually less aggressive than oral or nail-bed melanomas, which are particularly concerning. A new dark spot or lump in any of these locations earns a same-week appointment.

Soft Tissue Sarcomas

Soft tissue sarcomas arise from connective tissue. They tend to grow slowly and feel firm, painless, and well-defined under the skin, but they infiltrate surrounding tissue in ways that make complete surgical removal challenging. A harmless-looking lump that has been there for a year is exactly the kind of thing that turns out to be a soft tissue sarcoma.

Lipomas

Not all lumps are bad news. Lipomas are soft, movable fatty masses common in middle-aged and senior dogs and usually completely harmless. The catch is that lipomas can look identical to several aggressive cancers from the outside, which is why a quick fine-needle aspirate is worth doing before assuming a lump is just a fatty. These masses can grow so large that they impede movement, so may need to be removed even though they are benign.

Mast Cell Tumors

Mast cell tumors are one of the most common skin cancers in dogs and are notorious for looking like nothing at all, presenting as a small bump, a raised pink area, a hairless patch, or a lump that changes size from one day to the next. Cytology is the only way to tell, and early surgical removal usually has excellent outcomes.

Mammary Tumors

Canine mammary tumors occur most often in intact or late-spayed female dogs, and roughly half are malignant. Feline mammary tumors are less common but more aggressive, with the vast majority malignant. Spaying before the first heat cycle dramatically reduces mammary cancer risk in both species, and any swelling near the mammary chain warrants prompt examination.

Lymphoma

Lymphoma is one of the most common cancers in both dogs and cats. 1 in 15 dogs- and 1 in 8 Golden Retrievers specifically- will develop lymphoma. In dogs it most often presents as sudden, painless enlargement of multiple lymph nodes in an otherwise normal-looking pet.

In cats, lymphoma more often involves the gastrointestinal tract, with vomiting, weight loss, and appetite changes as the first signs. It is also one of the most chemotherapy-responsive cancers in veterinary medicine, which makes the treatment conversation meaningfully different from many other diagnoses.

Hemangiosarcoma

Hemangiosarcoma is an aggressive cancer of blood vessel walls, most often arising in the spleen, liver, or right side of the heart. It can grow silently for months and then announce itself through internal bleeding. Signs that need same-day emergency evaluation include sudden collapse or weakness, pale gums, abdominal distension, and labored breathing. Splenic hemangiosarcoma is one reason we recommend baseline abdominal imaging in senior dogs of higher-risk breeds.

Osteosarcoma

Osteosarcoma is the most common bone cancer in dogs, particularly large and giant breeds like Greyhounds, Rottweilers, Great Danes, and Saint Bernards. It causes persistent lameness or limb pain that does not fit a recent injury, sometimes with visible or palpable swelling at the affected bone. X-rays usually confirm the diagnosis quickly.

Squamous Cell Carcinoma

Squamous cell carcinoma affects skin and oral tissues. It is particularly common in cats with white fur on the ears, nose, and eyelids, where sun exposure contributes, and in the oral cavities of older cats. A persistent crusty or ulcerated area on a white cat’s nose or ear that will not heal needs prompt evaluation.

Which Warning Signs Warrant a Visit?

The signs of cancer in pets overlap with many less serious conditions, which is part of the problem. The reasonable rule is that any of these warrants a visit rather than an internet search:

  • A new lump or bump anywhere on or under the skin
  • An existing lump that has changed size, shape, color, or texture
  • Persistent sores that will not heal
  • Unexplained bleeding or discharge from any opening
  • Difficulty eating, swallowing, or breathing
  • Persistent lameness that does not fit a recent injury
  • Loss of appetite or unexplained weight loss
  • Lethargy, behavioral change, or decreased interest in normal activities
  • Persistent vomiting, diarrhea, or changes in urination or defecation

How Do We Diagnose Cancer in Dogs and Cats?

Cancer diagnosis is a layered process that starts with a physical exam and works toward the specific information needed to plan treatment. The goal is to move from “there is a lump” to “here is exactly what it is and how far it has gone.”

Bloodwork

Running a complete blood count and chemistry panel gives us a lot of information. For some cancers, like lymphoma in dogs, it can show the elevated white cell counts that are a classic sign. It can also point toward general places to look when we know something is wrong, but we’re not quite sure where. Blood panels help us differentiate from possible infections, immune mediated causes, or other diseases that can cause similar symptoms. If liver enzymes are elevated, we’ll proceed to liver imaging. If red blood cell counts are low, we will recommend imaging of the spleen. Many cancers don’t show up on bloodwork, and panels come back normal- which just tells us that we need to proceed to other types of testing to find the answers.

Fine Needle Aspiration and Biopsy

Fine needle aspiration is usually the first diagnostic step for a lump, using a small needle to collect cells that are evaluated under a microscope. The procedure is brief and minimally uncomfortable, and most pets do not need sedation. Cytology often answers the question in the same visit, distinguishing a reactive node, infection, lipoma, mast cell tumor, or lymphoma.

For deeper characterization or when cytology is inconclusive, a biopsy provides a larger sample under anesthesia. We may remove part of a mass or the entire thing, and biopsy gives us clues to the exact type of cancer, whether all of the tumor was removed or some cancer cells were left behind, and how malignant the cancer may be. Some tumors, like those in internal organs, require ultrasound guided biopsies or endoscopic biopsies. Arcata has a full suite of tools available, including ultrasound, endoscopy, and even the ability to provide laparoscopic organ biopsies, resulting in faster recovery times than traditional surgery.

Imaging and Cancer Staging

Once a cancer is diagnosed, staging tells us how far it has spread. Many cancers spread to the lungs, lymph nodes, and other organs, so staging directly informs the available treatment options. Ultrasound imaging, chest radiographs, and abdominal imaging assess internal organs and lymph nodes for evidence of spread. Our in-house imaging means most staging can be completed promptly, with access to board-certified radiologists for consultation.

Elderly Siamese cat undergoing a veterinary examination for cancer, emphasizing diagnosis, monitoring, and treatment of serious health conditions in senior pets.

What Are the Treatment Options for Pet Cancer?

Treatment plans are individualized based on the cancer type, stage, the pet’s overall health, and your goals, and several approaches are often combined.

Surgical Removal

For localized cancers, surgery is often curative when clear margins are achieved. Mast cell tumors, soft tissue sarcomas, and many oral tumors fall into the category where surgery is the primary treatment, and our surgical capabilities cover most oncologic surgeries in-house.

Chemotherapy

Veterinary chemotherapy is not the same experience as human chemotherapy. Doses are calibrated to minimize side effects while maintaining effectiveness, most pets continue normal activities through treatment, and hair loss is uncommon except in some breeds. For some cancers, chemotherapy is curative. For most, it just gives us more good time with our pets or achieves temporary remission. We’ll go through the options and outlook with you, and refer you to oncologists we trust if you want to go that route.

Radiation Therapy

Radiation therapy requires specialized equipment we don’t have on-site, so pets needing it are referred to radiation facilities we coordinate with. The most common applications are tumors that can’t be fully removed surgically, tumors in locations where surgery would be too damaging, and as follow-up after surgery when microscopic disease may remain. Modern veterinary radiation is much more targeted than it used to be, and most pets tolerate sessions well with brief anesthesia for each treatment.

Immunotherapy and Clinical Trials

Immunotherapy is one of the most promising emerging treatments, using the immune system to recognize and fight cancer cells, and is increasingly available for specific cancers like canine melanoma. Unlike chemotherapy, which attacks rapidly dividing cells broadly, immunotherapy trains the body to target cancer specifically, often with fewer side effects. The field is moving quickly, and new options for canine and feline cancers continue to emerge from veterinary research. Clinical trials are often available at various veterinary universities where research is performed. We’re happy to talk through whether immunotherapy or a clinical trial is part of the conversation for your pet’s specific diagnosis.

Supportive, Integrative, and Palliative Care

Not every cancer case is cure-focused. Keeping your pet comfortable through the process is a key part of treatment. We offer a variety of integrative care options like acupuncture that help many pets with pain, inflammation, and nausea.

When the goal shifts to comfort and quality time, our end-of-life care team provides nutritional guidance, pain management, and home care support, and we have a Certified Hospice and Palliative Care Veterinarian on staff. We’ll be with you every step of the way, help you assess your pet’s quality of life, and understand what the progression of their disease looks like.

Why Does Early Detection Matter?

The single most powerful tool in pet cancer is the routine wellness exam, because annual or semi-annual visits create a baseline that makes catching a change much easier. A lump documented at 5 mm for two years that is now 9 mm is information we can act on, while a lump no one has ever measured is only a question mark.

Early detection also expands treatment options. A small, early mast cell tumor often comes off with a clean surgical margin and never recurs, while a large, ulcerated one that has been there for a year is a more complicated conversation. The same logic applies across cancer types.

Frequently Asked Questions About Pet Cancer

Are Some Breeds More Likely to Get Cancer?

Several breeds are. Golden Retrievers, Boxers, Bernese Mountain Dogs, and others have higher rates of certain cancers, and large and giant breeds are at higher risk for osteosarcoma. Some risks are genetic while others relate to environmental and life-history factors, so breed predisposition is one piece of the picture rather than the whole picture.

Can I Prevent Cancer in My Pet?

Not entirely, but you can reduce risk meaningfully. Spaying before the first heat cycle dramatically lowers mammary cancer risk. Maintaining a healthy weight, providing year-round parasite prevention, limiting sun exposure for white-coated cats, and showing up for routine wellness visits all matter. Most importantly, catching cancer early through regular checks is what changes outcomes.

What Does It Feel Like to Find a Lump on My Pet?

It is understandable to feel anxious. The honest message is that many lumps turn out to be benign, and even when they are not, the path forward is usually clearer than the worry suggests. A quick fine-needle aspirate at a regular appointment answers most of the question, and the answer almost always opens more options than waiting does.

When You Spot Something, We’re Here

If you have found a lump, a sore that is not healing, or something about your pet that just feels off, you do not have to know what it is. Bring them in. Cytology and a careful exam often turn worry into a plan in a single visit, and when more workup is needed, we will walk through it with you.

Reach out to us to schedule a visit or talk through what you are seeing, and we will figure out the next step together.