Cancer Symptoms in Dogs: 7 Shocking Signs of Stomach, Lung, Bone & Liver Cancer

December 8, 2025 Admin

Catching cancer symptoms in dogs early can feel overwhelming and scary. Yet your attention and love may give your dog more time and better comfort. ❤️

Many cancers in dogs grow quietly at first. Owners often notice small changes that “don’t seem right” long before an obvious lump appears.

This guide walks you through seven surprising signs linked to stomach, lung, bone, and liver cancer. You’ll learn what to watch for, when to worry, and how to talk with your vet in a clear, confident way.

Nothing here replaces a veterinarian’s exam. It helps you notice patterns sooner, so you can act quickly and wisely.

Table of Contents

7 Shocking Cancer Symptoms in Dogs You Should Never Ignore

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Some warning signs of cancer in dogs can seem minor at first. You might notice a little weight loss, a mild cough, or a limp that comes and goes.

Below are seven key changes that deserve prompt attention, especially if they last more than two weeks or keep returning.

1. Sudden Weight Loss and Loss of Appetite

Unexplained weight loss is one of the most concerning changes. It often appears before other severe symptoms.

Your dog may still eat, yet seem to “melt away.” Or they may act hungry but lose weight anyway.

Why this can signal cancer

Tumors use up calories and nutrients.
Stomach and liver tumors can affect digestion and metabolism.
Pain or nausea can reduce appetite over time.

Stomach cancer symptoms in dogs often include:

Gradual or sudden weight loss
Eating less, stopping meals, or leaving food
Acting hungry but losing weight anyway

Liver cancer symptoms in dogs can show as:

Weight loss despite normal meals
Muscle loss along the spine and hips
A big, firm belly from an enlarged liver

Short example:
A 9‑year‑old Labrador started losing weight over two months. His owner noticed his ribs showing, even though he still ate. Bloodwork and an ultrasound later confirmed liver cancer.

When to call your vet
Contact your vet if:

Your dog loses weight over several weeks
You can suddenly see ribs, spine, or hip bones more clearly
Appetite changes last longer than a week

Early tests like bloodwork and an abdominal ultrasound can help rule out serious causes.

2. Ongoing Vomiting, Diarrhea, or Blood in Stool

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Most dogs get an upset stomach sometimes. But persistent tummy trouble is different. It can signal serious disease, including cancer.

Key signs to watch:

Vomiting more than once or twice a week
Diarrhea that lasts longer than three days
Dark, tar‑like stool (digested blood)
Bright red blood in stool or vomit

Stomach cancer symptoms in dogs often involve:

Repeated vomiting, sometimes with food or foam
Vomiting several hours after eating
Refusing food or walking away from the bowl
Black or bloody stool

According to information on stomach cancer symptoms in dogs from the American Kennel Club, chronic vomiting and weight loss are common warning signs:
https://www.akc.org/expert-advice/health/stomach-cancer-in-dogs/

Liver cancer can also affect digestion:

Intermittent vomiting and diarrhea
Poor digestion of fatty foods
Pale gums or yellow eyes if the liver is failing

Short example:
A 7‑year‑old mixed breed began vomiting every few days. Her owner blamed “sensitive stomach.” After a month, she developed black stool. An X‑ray and ultrasound later revealed a mass in her stomach.

When to call your vet
Seek a prompt exam if:

Vomiting or diarrhea continues beyond 24–48 hours
You see blood in vomit or stool
Your dog also seems weak, pale, or in pain

Your vet may suggest X‑rays, ultrasound, or endoscopy to check for tumors.

3. Chronic Coughing, Breathing Changes, or Wheezing

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A single cough after drinking water is usually harmless. Ongoing coughing or breathing trouble is not.

Lung cancer symptoms in dogs can be subtle at first, then worsen slowly.

Warning signs related to the lungs:

Coughing that lasts more than two weeks
Deep, dry, or hacking cough
Coughing more at night or after exercise
Faster breathing at rest
Open‑mouth breathing or wheezing

Lung cancer symptoms in dogs may include:

Coughing up blood or pink foam
Reluctance to play or run
Sudden collapse during activity

The Cornell University Hospital for Animals notes that lung tumors can cause a chronic cough, exercise intolerance, or breathing difficulty in affected pets:
https://www.vet.cornell.edu/hospitals/companion-animal-hospital/brochures/lung-tumors-dogs-and-cats

Short example:
A 10‑year‑old small breed dog developed a soft, regular cough. The owner assumed heart disease. Chest X‑rays later showed a single lung tumor.

When to call your vet
Get urgent veterinary help if your dog:

Coughs for more than a week
Struggles to breathe or breathes with effort
Breaths seem shallow, fast, or noisy

Your vet can take chest X‑rays, check oxygen levels, and rule out pneumonia, heart disease, or cancer.

4. Lameness, Swelling, or Bone Pain

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A limp after rough play may be a sprain. A limp that never fully resolves could indicate bone cancer.

Bone cancer symptoms in dogs often appear as:

Lameness that worsens over weeks
Swelling near a joint or along a limb
Pain when touching the area
Dog refusing to use the leg during walks

Large and giant breeds are at higher risk for bone cancer (osteosarcoma), especially in front legs. Yet any dog can develop it.

Typical bone cancer symptoms in dogs:

Progressive lameness with no clear injury
Hard, painful swelling that feels warm
Crying out when stepping or jumping

The American Veterinary Medical Association explains that osteosarcoma usually causes limb pain, swelling, and lameness in affected dogs:
https://www.avma.org/resources/pet-owners/petcare/osteosarcoma-dogs

Short example:
An 8‑year‑old Great Dane began limping on his front leg. Rest and pain medicine helped briefly. Two weeks later, a swollen, hard lump appeared above his wrist. X‑rays suggested bone cancer.

When to call your vet
Call your vet promptly if:

A limp lasts more than a week with no clear cause
You see a firm swelling on a limb
Pain medicines help less over time

Early imaging can help detect bone tumors and guide pain management.

5. A Bloated Belly, Jaundice, or Abdominal Pain

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A round belly can be harmless, especially in puppies or after a big meal. A firm, swollen abdomen in an adult dog is more concerning.

Liver cancer symptoms in dogs often include:

A large, bloated belly
Discomfort when you touch the abdomen
Reduced appetite or nausea
Weight loss with a bigger belly
Yellow eyes, gums, or skin (jaundice)

Tumors in the liver or spleen can bleed. This may cause sudden weakness, collapse, or very pale gums.

Stomach cancer may cause:

Audible gurgling, gas, or discomfort
Restlessness after eating
Burping, drooling, or stretching the front legs forward

Short example:
A 10‑year‑old Cocker Spaniel developed a round, tight belly. Her owner thought she was gaining weight. The scale showed weight loss, not gain. Ultrasound revealed a large liver mass.

When to call your vet
Seek urgent help if your dog has:

A suddenly big, hard, or painful belly
Pale gums, fast heart rate, or collapse
Yellow eyes or gums

These can be signs of bleeding tumors or advanced liver disease. Rapid treatment may save your dog’s life or relieve severe pain.

For more background on liver cancer symptoms in dogs, see this resource from VCA Animal Hospitals:
https://vcahospitals.com/know-your-pet/liver-tumors-in-dogs

6. Lumps, Skin Changes, or Non‑Healing Wounds

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Not every lump is cancer. Many are harmless fatty tumors. But new or changing lumps still deserve attention.

Concerning changes include:

A lump that grows quickly
A mass that feels fixed to underlying tissue
A sore that will not heal
A lump that bleeds, oozes, or ulcerates

How this connects to internal cancers

Skin tumors can be primary cancers.
Some internal cancers spread (metastasize) to skin or lymph nodes.
Enlarged lymph nodes can appear as firm lumps under the jaw or behind knees.

Short example:
A 9‑year‑old Beagle had a small, pea‑sized lump on his chest. It doubled in size within a month. A biopsy showed mast cell cancer, caught before it spread.

When to call your vet
Book an exam if you notice:

Any new lump lasting more than one month
A lump larger than a grape
A lump that changes color, shape, or texture

Your vet may do a fine needle aspirate. This simple test uses a tiny needle to sample cells for analysis.

7. Personality Changes, Lethargy, or Sudden Collapse

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You know your dog better than anyone. When their personality changes, pay attention.

General signs that can point to serious disease:

Sleeping far more than usual
Hiding, avoiding family, or seeming withdrawn
Growling when touched in certain spots
Sudden loss of interest in walks or play

These are not specific to cancer. Yet they often appear when a dog feels unwell, in pain, or weak.

Sudden collapse can occur with:

Bleeding tumors in the spleen or liver
Lung tumors causing blood clots
Advanced bone cancer after a pathologic fracture

Short example:
A 12‑year‑old mixed breed stopped greeting his owner at the door. He began avoiding stairs and seemed “down.” Blood tests and imaging revealed a bleeding tumor on his spleen.

When to call your vet
Call your vet soon if you notice:

A clear change in energy that lasts over a week
Ongoing reluctance to move, jump, or be touched
Any fainting, collapse, or seizure

These signs deserve a full physical exam and basic lab tests at minimum.

Quick Reference: What Different Symptoms May Suggest

Use this chart as a simple guide when you notice changes. It is not a diagnosis. Always rely on your vet for that.

Symptom	Possible Cancer Location	How Urgent Is It?
Weight loss, poor appetite	Stomach, liver, many other organs	See vet within a few days
Chronic vomiting or bloody stool	Stomach, intestines, liver	See vet within 24–48 hours
Persistent cough or breathing changes	Lungs, chest	See vet quickly; same day if breathing is hard
Lameness, limb swelling, bone pain	Bones (osteosarcoma)	See vet within a few days or sooner if severe
Bloated, painful abdomen	Liver, spleen, stomach	Emergency if sudden or with pale gums
Fast‑growing lump or non‑healing sore	Skin, lymph nodes, metastasis	See vet within a week
Collapse, extreme weakness	Bleeding tumors, advanced disease	Immediate emergency care

How Vets Detect and Confirm Cancer in Dogs

If your vet suspects cancer, they will combine history, exam findings, and tests. Knowing what to expect can ease some fear.

Common diagnostic steps:

Full physical exam and detailed history
Bloodwork and urine tests
X‑rays of chest, limbs, or abdomen
Ultrasound of the belly
Fine needle aspirate of lumps or lymph nodes
Biopsy to examine tissue under a microscope

For lung cancer symptoms in dogs, your vet may order chest X‑rays or a CT scan. For stomach cancer and liver cancer, abdominal ultrasound and endoscopy can help.

Bone cancer diagnosis often starts with limb X‑rays. Sometimes further imaging or a bone biopsy confirms the type of tumor.

Treatment Options and Quality of Life

Hearing the word “cancer” for your dog is heartbreaking. Yet many dogs still enjoy meaningful, comfortable time with their families after diagnosis.

Treatment choices depend on:

The type of cancer
Where it is located
Whether it has spread
Your dog’s age and other health issues
Your family’s budget and wishes

Common treatment options:

Surgery to remove lumps or tumors
Chemotherapy using dog‑safe protocols
Radiation therapy for certain tumors
Targeted therapies for specific cancers
Palliative care to control pain and nausea

For example:

Some bone cancers may need limb amputation plus chemotherapy.
Early liver tumors may be removed surgically.
Single lung tumors can sometimes be taken out, giving good time.

Discuss your priorities openly with your vet or a veterinary oncologist. Many families choose a focus on comfort and gentle care. Others pursue advanced treatment. Both paths can be loving and responsible.

Supporting Your Dog Emotionally and Physically

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Dogs with cancer still enjoy many simple pleasures. Your support matters every day.

Practical ways to help:

Keep a daily journal of appetite, energy, and mood.
Offer soft beds and non‑slip flooring for weak dogs.
Warm, bland meals may help with nausea, if your vet agrees.
Short, gentle walks keep joints loose and minds engaged.

Emotional support for you and your family:

Ask your vet honest questions about prognosis and comfort.
Seek a support group for pet loss or chronic illness.
Involve children in age‑appropriate ways, letting them say goodbye.

Your bond with your dog does not end with a diagnosis. Many families share deeply meaningful months or years after discovering cancer.

FAQs About Cancer Symptoms in Dogs

1. What are the earliest cancer symptoms in dogs I might notice at home?

Early signs often include mild weight loss, subtle appetite changes, or lower energy. You may also notice a soft limp, a small new lump, or a slight cough. Any change that persists for more than two weeks deserves a vet visit.

2. How are stomach cancer symptoms in dogs different from usual tummy upset?

Typical tummy upset improves within one or two days. Stomach cancer symptoms in dogs often involve chronic or frequent vomiting, weight loss, and poor appetite over weeks. Black, tarry stool or blood in vomit is especially concerning and needs prompt care.

3. Are lung cancer symptoms in dogs always obvious, like a strong cough?

Not always. Some dogs with lung tumors have only mild coughing or decreased tolerance for exercise at first. Others may show faster breathing at rest or subtle wheezing. Any cough lasting longer than two weeks should be checked.

4. How can I tell if a limp is from injury or bone cancer?

A mild injury often improves with a few days of rest. Bone cancer symptoms in dogs usually get worse over time, not better. You may feel a firm swelling near a joint, and pain medicine may help less as weeks pass. Persistent lameness always needs imaging.

5. What specific signs point to liver cancer symptoms in dogs?

Common liver cancer symptoms in dogs include weight loss, a firm swollen belly, reduced appetite, and sometimes vomiting or diarrhea. Yellow gums or eyes (jaundice) and pale gums can occur in advanced cases. These are urgent signs and need veterinary care quickly.

6. Can cancer symptoms in dogs be caused by less serious problems instead?

Yes. Many of these signs can result from infections, autoimmune disease, injuries, or other conditions. That is why a veterinary exam is essential. No article can tell you for sure. Your vet’s job is to rule out or confirm cancer and guide the next steps.

When You Notice Cancer Symptoms in Dogs: What to Do Next

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Noticing possible cancer symptoms in dogs is frightening, yet it also shows how much you care. Your attention can lead to faster diagnosis, better pain control, and more time together.

If you see persistent weight loss, chronic vomiting, ongoing cough, limping, a swollen belly, or changing lumps, do not wait. Call your veterinarian and describe exactly what you have observed. Mention any patterns that match stomach cancer symptoms in dogs, lung cancer symptoms in dogs, bone cancer symptoms in dogs, or liver cancer symptoms in dogs.

Bring photos, videos, and a written list of symptoms to your appointment. That information helps your vet see the full picture.

You are your dog’s voice. By watching closely, asking questions, and acting early, you give your dog the best chance for comfort, dignity, and quality time by your side. 💗