Lump on a Cat's Belly or Side: Causes and Next Steps

Name: Lump on a Cat's Belly or Side: Causes and Next Steps
Creator: Dr. Zubair Khalid

By Dr. Zubair Khalid, DVM, MS, PhD · 2026-10-03

A cat lump on the abdomen is a common finding, and most turn out to be harmless fat deposits or small skin growths. Some lumps, though, come from deeper organs inside the belly and can only be felt once they are fairly large. The sections below help you tell the difference and decide how fast to act.

This article is educational and is not a substitute for veterinary diagnosis or treatment.

Quick Answer

A soft, movable lump under the skin is often a lipoma, a benign fatty tumor that is most common on the abdomen in cats [1].
A warm, painful, fast-growing lump may be an abscess or infected pocket and needs same-day veterinary care.
A lump you can feel deep in the belly, especially with weight loss, vomiting, or appetite changes, needs prompt imaging.
Never squeeze, poke, or try to drain a lump at home.
Take a photo, note the size and date, and book a vet visit. Early evaluation is the safest path.

What a Lump on a Cat's Belly or Side Usually Looks Like

Owners often describe a cat lump on the tummy as a pea, a marble, or a golf ball under the skin. Some are flat and soft. Others feel firm or irregular. Some sit right under the skin and move freely when you touch them. Others feel attached to deeper tissue and barely move at all.

It helps to sort lumps into two groups.

Skin-level lumps sit in or just under the skin. You can usually pinch the skin around them. These include fatty tumors, cysts, and small growths.

Deeper abdominal masses sit inside the belly wall or among the organs. You feel them through the abdominal wall, like a firm object behind a thin blanket. These are harder to judge by touch alone.

Normal belly anatomy can also confuse things. Cats have a small fat pad, lymph nodes, and organs that can feel lumpy depending on body condition. A thin cat's kidneys and intestines are easier to feel than a chubby cat's. That is one reason a hands-on exam matters.

If the swelling is broad and soft instead of a distinct lump, see Cat Swollen Belly Causes for a fuller picture.

Main Causes of a Cat Lump on the Abdomen

Cause	Typical clues	How urgent
Lipoma (benign fatty tumor)	Soft, movable, often multiple, most common on the abdomen [1]	Routine visit
Hemangioma (benign blood vessel tumor)	Red to black, round, may look like a blood blister, can ulcerate and grow large [1]	Prompt visit
Abscess or infected pocket	Warm, painful, swelling, fever, lethargy, may drain	Same day
Mammary tumor	Firm lump along the milk chain on the belly or chest [2]	Prompt visit
Abdominal organ mass	Deep, firm, felt through the wall, often with weight loss or vomiting	Prompt to urgent
Fluid-filled cyst or cavity	Soft, squishy, may fluctuate in size	Prompt visit
Lymphoma or other round cell tumor	Deep mass, thickened bowel or stomach wall, enlarged lymph nodes [3]	Urgent

Lipomas

Lipomas are benign tumors of fatty tissue. They are occasionally found in cats, and older neutered male Siamese cats are most at risk. They are most commonly found on the abdomen. Obesity does not appear to be a factor in their development in cats [1].

These lumps usually feel soft and discrete, and most move freely when touched. Multiple lipomas may be present. Many merge with the healthy fat next to them, which makes it hard for a veterinarian to find the edge of the tumor by feel alone [1].

Hemangiomas

Hemangiomas are single or multiple round lumps that range from red to black. They resemble blood vessels, and some look like blood blisters. They are uncommon tumors of adult cats and most often develop on the head, legs, and abdomen. They are benign, but they tend to ulcerate and grow quite large. Surgical removal is the treatment of choice, and freezing or radiation may be needed if the tumor is large or on the lower legs. These tumors do not usually spread after complete surgical removal [1].

Abscesses and infected pockets

An abscess is a walled-off pocket of pus. It often follows a bite, scratch, or puncture wound. The area feels warm and tender, and your cat may flinch when you touch it. Some abscesses burst and drain on their own. Others need to be opened, flushed, and treated with antibiotics.

Abscesses are not limited to the skin. A cat can develop an abscess deep inside the abdomen. One report described a 13-year-old cat with recurrent pancreatic abscesses that caused weight loss, increased appetite, increased thirst and urination, and intermittent vomiting. The cat also had diabetes mellitus. The infection persisted through months of antibiotics and repeated drainage and eventually ruptured, causing septic peritonitis [4]. This shows how serious a deep abdominal infection can become.

Mammary tumors

Cats have mammary tissue running along both sides of the belly and chest. A firm lump in that chain may be a mammary tumor [2]. These can be benign or malignant, and they are more common in unspayed females, though any cat can develop one. Because the tissue is right under the skin, owners often find these lumps early.

Deeper abdominal masses

Masses that start in organs such as the liver, pancreas, intestine, or lymph nodes may not be felt until they are large. Signs often include vomiting, poor appetite, weight loss, or a visibly distended belly.

One case report described a 7-year-old neutered male cat with weeks of vomiting, loss of appetite, and abdominal distension. Blood work showed a cholestatic pattern with high alkaline phosphatase and gamma-glutamyl transferase. X-rays showed a cranial abdominal mass, and ultrasound found a multiloculated cyst with thin septa and no mural nodules. CT confirmed a very large cystic liver mass. Surgery removed it completely while preserving liver tissue [5].

Lymphoma is a common cancer in cats, and the alimentary form often affects the stomach and intestines. In one study of cats infected with feline leukemia virus, the small intestine was the most common site, followed by the large intestine and stomach. Multiple parts of the digestive tract were affected in most cases. Thickening of the intestinal and gastric walls was the most common finding, and mural nodules were seen in half the cats. The mesenteric lymph nodes were often involved too [3].

Other cancers can also appear as masses. Plasma cell neoplasia is uncommon in cats, and one report described a 14-year-old cat with multicentric disease that responded to radiation and chemotherapy [6]. A separate report described a rare tracheal squamous cell carcinoma in a 7-year-old cat with breathing trouble [7]. These are different locations, but they show that not every mass is in the belly and not every mass is cancer of the same type.

Red Flags That Make It an Emergency

Call an emergency clinic right away if you see any of these.

Your cat is struggling to breathe, breathing fast at rest, or has blue gums.
The belly is hard, swollen, and painful, and your cat cries when touched.
Your cat is collapsing, weak, or unresponsive.
There is heavy bleeding from the lump.
The lump burst and is draining foul-smelling fluid with fever or lethargy.
Your cat is vomiting repeatedly and cannot keep water down.
You see pale gums, a racing heart, or a distended belly after a known or suspected rupture.

A ruptured deep abscess can cause septic peritonitis, which is life threatening [4]. This is a surgical emergency, not a wait-and-see problem.

For a broader look at belly swelling and when it signals danger, see Why Is My Cat's Belly Swollen?.

Safe Things You Can Do at Home While You Wait

You cannot diagnose a lump at home, but you can gather useful information.

Measure the lump with a ruler and write down the size and date.
Take clear photos from two angles in good light.
Note whether it is soft or firm, movable or fixed, and whether it is warm or painful.
Check for other lumps on the belly, chest, legs, and head.
Watch for appetite, drinking, vomiting, diarrhea, weight loss, and energy changes.
Keep your cat indoors and away from other animals if the lump might be an abscess.
Do not squeeze, lance, or apply heat or ice to the lump.
Do not give human pain relievers. Many are toxic to cats, and the dose must be calculated by a veterinarian based on your cat's weight and health.

If the lump is small, soft, and your cat is acting normal, a routine visit within a week or two is reasonable. If it is growing, painful, or your cat seems unwell, move faster.

What the Veterinarian Will Check and Test

Your vet starts with a full physical exam. They will feel the lump and compare it to the other side. They will check its size, texture, mobility, and whether it seems attached to deeper tissue. They will also feel the belly for organ enlargement, fluid, or other masses, and check lymph nodes and body condition.

Then they decide whether the lump is skin-level or deeper.

For skin-level lumps, a common next step is a fine needle aspirate. The vet inserts a thin needle into the lump, pulls out cells, and looks at them under a microscope. This can often tell a fatty tumor from an infection or a round cell tumor. If the result is unclear, they may recommend a biopsy or surgical removal.

For deeper masses, imaging is usually needed. Ultrasound is the first choice because it shows the shape, texture, and blood flow of organs and masses. It can show whether a mass is solid, cystic, or mixed. X-rays can show a large mass or displacement of organs. In some cases, contrast-enhanced CT or MRI gives a more detailed map before surgery or treatment [5][6].

Blood work helps too. It can show anemia, infection, organ changes, or a cholestatic pattern when the liver or bile ducts are involved [5]. If lymphoma is suspected, the vet may sample lymph nodes or the bowel wall.

Not every lump needs surgery. A small lipoma may just be monitored. A suspicious mass is usually removed or sampled because the only way to know the exact type is to look at the tissue under a microscope [1].

If your cat has several lumps or a rash with bumps, see Cat Skin Bumps and Lumps: When to See a Vet and When to Monitor and Cat Skin Rash with Bumps: Common Causes and Next Steps.

Prevention and Monitoring

You cannot prevent every lump, but you can catch problems early.

Do a monthly hands-on check. Run your fingers over the belly, sides, chest, legs, and neck.
Record the date, size, and location of any new lump.
Watch for changes in size, shape, color, or texture.
Watch for ulcers, bleeding, or drainage.
Keep your cat at a healthy weight and up to date on veterinary care.
Spaying reduces the risk of mammary tumors [2].
Keep FeLV and other infectious disease prevention current, since some cancers are linked to viral infection [3].
If your cat has a known lipoma, recheck it at each exam. Lipomas can merge with normal fat and become harder to measure over time [1].

A lump that stays the same size for months is less worrying than one that doubles in a few weeks. Growth, pain, and illness signs are the main reasons to move up a visit.

Limitations and When to Contact a Veterinarian

No article can tell you what a specific lump is. Only a veterinarian who examines your cat can do that, and sometimes only a lab can confirm the type.

Contact a veterinarian the same day if the lump is new and painful, warm, red, or draining, or if your cat has a fever, poor appetite, or low energy.

Go to an emergency clinic now if your cat is having trouble breathing, has a hard and painful belly, is collapsing, has heavy bleeding, or has a burst lump with signs of shock.

Schedule a routine visit within one to two weeks if the lump is small, soft, movable, and your cat is eating, drinking, and acting normally.

If you are unsure, call your vet's office and describe what you found. They can help you decide how soon to come in.

Frequently Asked Questions

Is a lump on my cat's belly always cancer?

No. Many belly lumps are benign fatty tumors called lipomas, and others are cysts or abscesses [1]. That said, some lumps are cancerous, so a vet exam is the only way to know. Early evaluation gives the best options.

Can I tell if a lump is a lipoma by touching it?

Not reliably. Lipomas often feel soft and movable, but many merge with the healthy fat around them, which makes the edges hard to find even for a veterinarian [1]. A needle sample or biopsy is needed for a firm answer.

Should I wait and see if the lump goes away?

It depends on the lump. A small, soft lump in a cat that feels well can often be watched for a short time. A lump that is growing, painful, or paired with vomiting, weight loss, or appetite changes should be checked soon.

What if the lump is deep inside the belly and not under the skin?

A deep mass is felt through the abdominal wall and usually needs imaging such as ultrasound or CT to see what it is attached to [5][6]. Your vet may also run blood work. Some deep masses are benign cysts, and others are tumors or infections.

Can a lump on the side of the stomach be a sign of something serious?

Yes, it can be. A firm lump on the flank or side may come from an organ, a lymph node, or the body wall. Signs like weight loss, vomiting, or a swollen belly raise concern and mean you should book a visit promptly.

References

Tumors of the Skin in Cats - Cat Owners. Merck Veterinary Manual.
Mammary Tumors in Cats - Reproductive System. Merck Veterinary Manual.
Pathological characterization of lymphomas with involvement of the alimentary tract in feline leukemia virus-infected cats. Veterinary pathology, 2026.
Recurrent pancreatic abscesses coexisting with a suspected adenocarcinoma in a cat. JFMS open reports, 2026.
Giant Hepatobiliary Cystadenoma Requiring Biliary Reconstruction in a Cat: A Case Report. Veterinary medicine and science, 2026.
Multicentric Round Cell Neoplasia with Plasmacytic Differentiation in a Cat with Systemic Progression: Multimodal Imaging and Treatment Response. Animals : an open access journal from MDPI, 2026.
Tracheal Squamous Cell Carcinoma in an Adult Cat. Veterinary radiology & ultrasound : the official journal of the American College of Veterinary Radiology and the International Veterinary Radiology Association, 2026.