You are scratching your dog’s chest and your fingers find something new: a soft lump under the skin, a small raised bump, or a pink button on a leg. It is natural to worry.
Many lumps turn out to be harmless. But some are not, and the most important fact for owners is this: you cannot tell what a lump is by looking at it or feeling it. A review of canine cancer data from Portugal points out that in dogs the chance a new lump is cancer is roughly as high as the chance it is harmless, so every new mass deserves a proper check. [1]
Have a cat? See our guide to lumps and bumps on cats.
How common are skin lumps in dogs?
Very common. In a large Italian animal cancer registry, the skin was the most frequent site of tumors in dogs, at about 38% of all cases, with soft tissue under the skin in third place. [2]
Cancer in general is also common in dogs. The American Veterinary Medical Association (AVMA) estimates that about 1 in 4 dogs will develop cancer at some point in their life, rising to 1 in 2 for dogs 10 years or older. [3] That is why every new lump deserves a check.
Benign vs malignant: what the words mean
The AVMA explains the difference: [3]
- Benign growths are not cancer. They usually grow slowly, push surrounding tissue aside rather than invading it, and do not spread through the body. They usually do not threaten a pet’s life unless they press on important structures. Lipomas (fatty tumors) and sebaceous adenomas are common examples.
- Malignant growths are cancer. They can grow at different rates, sometimes fast, invade nearby tissue, and can spread (metastasize) to other parts of the body.
Common lumps vets see
Lipomas (fatty lumps)
Lipomas are benign tumors of fat and are common in dogs. [1][4] In the Italian registry, fatty tumors were the largest group among tumors of the soft tissue under the skin. [2] A large UK study of more than 384,000 dogs under veterinary care found that about 1.9% were diagnosed with a lipoma in one year. [4]
Key risk factors from that study: [4]
- Age: dogs aged 9 to under 12 years had 17.5 times the odds of lipoma compared with dogs aged 3 to under 6.
- Body weight: dogs at or above the average adult weight for their breed and sex had about twice the odds. The authors suggest being overweight may predispose dogs to lipomas.
- Breed: the highest prevalence was in Weimaraners (7.8%), Dobermann Pinschers (7.0%), German Pointers (5.2%), Springer Spaniels (5.2%) and Labrador Retrievers (5.2%).
Even when a lump feels like a typical fatty lump, your vet will usually want to confirm it, because a lump’s look and feel cannot tell a harmless growth from a cancerous one. [1]
Histiocytomas (young dogs)
Histiocytomas are common benign skin tumors and the most common skin growth in young dogs: dogs of any age can get them, but most cases are in dogs under four years old. [5] They usually appear as a single, fast-growing, red, raised, hairless bump shaped like a button, most often on the head (especially the ears), the limbs, the nose or the scrotum. [5] They rarely spread, and they usually shrink and disappear on their own within weeks to months. [5]
Sebaceous adenomas (older dogs)
These are benign growths of the oil glands in the skin. The AVMA lists them, with lipomas, as common examples of benign growths in pets. [3]
Mast cell tumors
Mast cell tumors are important to know about. They are the most often diagnosed malignant skin tumor in dogs, making up about a fifth of all canine skin tumors. [6] Their behavior ranges widely, from fairly harmless to aggressive, and only lab tests (cells under the microscope and grading of the removed tissue) show which kind a dog has. [6] Older dogs are not the only ones at risk: mast cell tumors are also the most common malignant skin tumor in young dogs, and in young dogs they can be confused with harmless histiocytomas. [7] This is a major reason why vets test lumps rather than judging by appearance.
A soft, painless swelling on the point of the elbow in a large dog may be a fluid-filled sac rather than a growth; see elbow hygroma in dogs.
How your vet checks a lump
Fine needle aspirate (cytology)
The usual first step is a fine needle aspirate: your vet uses a thin needle to collect cells from the lump and looks at them under a microscope or sends them to a lab. [3][6] It is quick, usually done without sedation, and often gives a clear answer.
How reliable is it? In a study comparing needle samples with full tissue biopsies from 292 skin and under-the-skin lumps in 242 dogs and 50 cats: [8]
- About 83% of needle samples had enough cells to read.
- Among those readable samples, the needle result agreed with the biopsy in 90.9% of cases.
- When the needle sample said “tumor,” it was right 99.4% of the time.
- When it said “not a tumor,” it was right only 68.7% of the time.
In other words, a needle sample is very good at confirming a tumor, but a “not a tumor” result is less certain. If the result is unclear, or the lump keeps growing, your vet may recommend a biopsy.
Biopsy
A biopsy removes a small piece of tissue, or the whole lump, for a pathologist to examine. The AVMA notes that for many tumors a biopsy is often necessary to confirm the diagnosis and determine whether the tumor is benign or malignant. [3]
Further tests
If a lump is cancerous, the AVMA notes that samples from other tissues, such as nearby lymph nodes, may be needed to find out whether and how far the cancer has spread. [3]
Treatment
Treatment depends on what the lump is:
- Not every benign lump has to come off. Your vet may suggest keeping an eye on a confirmed harmless lump that is not sore, growing or in the way.
- Most histiocytomas go away on their own. [5]
- For skin cancers, surgical removal is a main treatment, and the plan depends on the tumor type, its size, where it is and whether it has spread. [6] For low grade mast cell tumors, the outlook after complete removal is good. [7]
- Cancers may also be treated with chemotherapy, radiation or other therapies, sometimes with a veterinary oncologist. [3][6]
Warning signs: when to see your vet promptly
The AVMA lists general warning signs of cancer in pets, including: [3]
- Lumps or bumps that grow or change color or texture over time
- Persistent sores or wounds that won’t heal
- Unexplained swelling, heat, pain or lameness
- Loss of appetite or unexplained weight loss
- Bleeding from the mouth, nose or other body openings
If you notice any of these, the AVMA advises contacting your veterinarian right away; several of these signs also occur with non-cancer conditions, but they still need checking. [3]
A simple lump-tracking routine
You can help your vet by keeping track:
- Check your dog all over once a month, during grooming or a belly rub.
- Note each lump’s location, size and feel. Measure it with a ruler (or compare it to a coin) and take a dated photo.
- Book a check for any new lump, and go sooner if it is growing, changing, red, ulcerated or bothering your dog.
- Do not squeeze or pop lumps. Some tumors, including mast cell tumors, can become inflamed when handled roughly.
Frequently asked questions
Are most lumps on dogs cancer?
Many are benign, such as lipomas, histiocytomas and sebaceous adenomas. [3][5] But the skin is the most common site of tumors in dogs, mast cell tumors are a common malignant type, and you cannot tell them apart by touch. [1][2][6] Have every new lump checked.
Can a vet tell what a lump is just by feeling it?
Not reliably. Harmless and cancerous lumps can look and feel alike, so a needle sample or biopsy is usually needed to know what a lump is. [1][3][6]
Does a needle sample hurt my dog?
Most dogs tolerate it well, similar to a vaccination. It is usually done during a normal appointment without sedation.
My dog has a fatty lump. Does it need to be removed?
Not always. A confirmed harmless lump that is not sore, growing or in the way may simply be watched. Your vet will usually confirm it is a lipoma first, and may suggest removal if it grows large, is in an awkward place, or bothers your dog. Keeping your dog at a healthy weight may help, since heavier dogs had higher odds of lipoma in a large study. [4]
My young dog has a pink bump on the ear. What is it?
It could be a histiocytoma, a usually benign growth common in young dogs that often appears on the head, ears or limbs and usually goes away on its own within weeks to months. [5] Because other growths, including mast cell tumors, can look similar, have it checked. [7]
What are the warning signs that a lump could be cancer?
The AVMA lists lumps that grow or change color or texture, sores that won’t heal, and unexplained swelling, heat, pain or lameness among the warning signs of cancer. [3] See your vet promptly.
The bottom line
Lumps are very common in dogs, and many are harmless, but you cannot tell which by touch. A quick needle sample is the usual first test, with a biopsy when needed. Track lumps at home, and see your vet for any new lump, and promptly for one that grows, changes or ulcerates.
See your vet for every new lump, and promptly if it is growing, changing, bleeding, or your dog seems unwell.
This article is for general information only and is not a substitute for professional veterinary advice, diagnosis or treatment. Always consult your veterinarian about your pet’s health. If you think your pet has a medical emergency, contact your veterinarian or an emergency animal hospital right away.
Sources
- Brilhante-Simões P, Lopes R, Delgado L, et al. Every Tumour Counts: A Comprehensive Overview of Canine Oncology in Portugal. Animals. 2025;16(1):35. doi:10.3390/ani16010035 (CC BY 4.0). https://pmc.ncbi.nlm.nih.gov/articles/PMC12784951/
- Carnio A, Cocumelli C, Galietta V, et al. The epidemiological landscape of canine tumors in central Italy: animal cancer registry insights, distribution patterns, and incidence estimates. Frontiers in Veterinary Science. 2026;13:1919722. doi:10.3389/fvets.2026.1919722 (CC BY 4.0). https://pmc.ncbi.nlm.nih.gov/articles/PMC13594995/
- American Veterinary Medical Association. Cancer in Pets (client brochure, 2025). https://ebusiness.avma.org/files/productdownloads/mcm-clientbroch-cancer-in-pets-2025.pdf ; https://www.avma.org/resources/pet-owners/petcare/cancer-pets
- O’Neill DG, Corah CH, Church DB, Brodbelt DC, Rutherford L. Lipoma in dogs under primary veterinary care in the UK: prevalence and breed associations. Canine Genetics and Epidemiology. 2018;5:9. doi:10.1186/s40575-018-0065-9. https://pmc.ncbi.nlm.nih.gov/articles/PMC6161450/
- Pires I, Rodrigues P, Alves A, Silva F, Lopes C. Histopathological and Ultrastructural Study of a Canine Langerhans Cell Tumour (Canine Cutaneous Histiocytoma). Cells. 2024;13(15):1263. doi:10.3390/cells13151263 (CC BY 4.0). https://pmc.ncbi.nlm.nih.gov/articles/PMC11312119/
- Mârza SM, Munteanu C, Papuc I, Purdoiu RC. Comparative pathophysiology and molecular insights into cutaneous and non-cutaneous canine skin cancers: focus on melanoma, mast cell tumors, and squamous cell carcinoma. Frontiers in Immunology. 2025;16:1624598. doi:10.3389/fimmu.2025.1624598 (CC BY 4.0). https://pmc.ncbi.nlm.nih.gov/articles/PMC12695799/
- Schwinn J, Törner K, Beitzinger C, Klopfleisch R, Aupperle-Lellbach H. The Characteristics of 924 Cutaneous Mast Cell Tumours in Dogs ≤ 3 Years of Age. Veterinary Sciences. 2026;13(5):500. doi:10.3390/vetsci13050500 (CC BY 4.0). https://pmc.ncbi.nlm.nih.gov/articles/PMC13211724/
- Ghisleni G, Roccabianca P, Ceruti R, et al. Correlation between fine-needle aspiration cytology and histopathology in the evaluation of cutaneous and subcutaneous masses from dogs and cats. Veterinary Clinical Pathology. 2006;35(1):24-30. doi:10.1111/j.1939-165x.2006.tb00084.x. https://pubmed.ncbi.nlm.nih.gov/16511787/