By the Pethocyn editorial team. Published October 28, 2026. Updated November 2, 2026. Sources are listed at the end of the article.

Lumps in and under the skin are among the growths vets see most often in cats. In a national survey of feline tumors in Portugal, skin and soft tissue tumors made up about 42% of cases, second only to mammary tumors, and this group held a larger share of benign growths than most others. [1]

This guide covers what skin tumors in cats can look like, how vets tell them apart, the main types, and the rule vets use for lumps at a vaccination site. For dogs, see lumps and bumps on dogs.

Not every skin tumor is a lump

A skin tumor can be a raised lump, but some begin in other ways. Sun damage can first show as red, thickened, scaly patches (actinic keratosis), which can go on to become cancer. [9] In a group of cats with skin squamous cell carcinoma, more than half of the tumors were eroding the skin rather than simply forming a bump. [8] Because growths vary so much in how they look, only a vet can work out what a new lump, patch or sore is.

Benign or cancerous? Only tests can tell

  • Benign growths stay where they are. Many of the skin tumors cats and dogs get from the outer layers of the skin fall into this group. [2]
  • Malignant (cancerous) growths can push into nearby tissue, come back after removal, and in some cases spread. [10][11]

To find out which kind a lump is, a vet can draw cells out with a thin needle (fine needle aspiration) or remove a piece of tissue (a biopsy). In a study of 292 skin and under-the-skin lumps from dogs and cats, the needle sample agreed with the lab’s tissue diagnosis in about 91% of usable samples, though some samples held too few cells to read and some tumors were missed, which is why a biopsy is sometimes still needed. [3]

After a growth is removed, a pathologist checks the edges of the removed tissue (the surgical margins) for tumor cells. That result, together with the type of tumor, helps your vet decide whether more treatment is needed. [4]

Some of the skin tumors cats get

These are some of the types that show up often in cat studies, plus the tumor that can form at injection sites. Many other kinds exist.

Basal cell tumors

Basal cell tumors come in a benign form (now called trichoblastoma) and a malignant form (basal cell carcinoma). In a Lithuanian lab study, they made up just under 5% of tumors in cats, and almost two thirds of the feline cases were the malignant form, a higher share than in dogs. [5] So a lump of this kind still needs a lab result before anyone can say how it will behave.

Mast cell tumors

Mast cell tumors are the second most common skin tumor in cats. [7] They are less common in cats than in dogs, the skin form in cats usually shows up on the head and neck, and up to 1 in 5 affected cats has more than one. Cats with several of these tumors tend to do worse than cats with a single one. [6] A review notes the skin form tends to behave more mildly in cats than in dogs. [2]

Young Siamese cats under 4 may be more likely to get an “atypical” type of skin mast cell tumor. [6]

In a UK study of 287 mast cell tumor records sent to a diagnostic laboratory, the median age of the cats was 11 years. Siamese, Burmese, Russian Blue and Ragdoll cats were more susceptible. The head was the most common site in younger cats, and the trunk in older cats. Of 69 cats with known outcomes, 12 (17.4%) died of the tumors. [7]

Squamous cell carcinoma and sun damage

Squamous cell carcinoma of the skin is one of the most frequent skin tumors in cats. It is linked to lightly pigmented skin and long-term sun exposure. Most cases can be cured, but some cats get a more aggressive form that invades nearby tissue and comes back. [8] In one group of 33 affected cats, every cat had a white or partly white coat, and the tumors sat on the nose, ears, eyelids and lips, with the nose the most common spot. [8]

Ultraviolet light is a known cause of these tumors, and the red, scaly sun-damaged patches mentioned above can come first. [9] Pale skin with thin hair cover, such as the nose and ear tips, is most at risk. [9] Keeping high-risk cats out of the sun during the hours of strongest UV is the usual advice, and UV still reaches a cat lying in a sunny window. [9] Ask your vet before putting anything on your cat’s skin for sun protection: a 2026 review found little research on how safe or effective sunscreens are for pets. [9]

Injection-site sarcomas

Soft tissue sarcomas are among the most common skin tumors in cats. [11] One kind, the feline injection-site sarcoma, is a malignant tumor that most often forms where vaccines are given, and it has also been seen at sites of other injections, injuries or microchips. [10] Typical sites include the area between the shoulder blades, the side of the chest or belly wall and the lower back. [11] These tumors can take a long time to appear, then grow fast and push deep into nearby tissue, although they spread to other organs less often. [10] They are hard to remove in full: a study notes that they come back after surgery in almost 60% of cases. [11] In a survey of feline tumors, the high number of fibrosarcomas was partly put down to this tumor type. [1]

Keep the risk in proportion. A 2026 review of 8 studies covering more than 14 million vaccinations estimated about 1 case per 10,000 vaccinations, while rating the certainty of the evidence as very low. The authors concluded the tumor remains a rare adverse event and that the results reinforce the importance of routine vaccination. [12] Your vet can recommend the vaccines and schedule that suit your cat’s age, health and lifestyle.

The 3-2-1 rule for lumps after a vaccine

The AAHA/AAFP feline vaccination guidelines recommend that vets and owners watch the vaccination site for swelling or lumps using the “3-2-1” rule. A biopsy of a lump is warranted if it: [13]

  • 3: is still there 3 months after vaccination,
  • 2: is larger than 2 cm (about 3/4 inch) across, or
  • 1: is getting bigger 1 month after vaccination.

The guidelines add that local inflammation at the injection site is among the most commonly reported vaccine reactions. [13] So a small lump after a shot is worth watching, and the 3-2-1 rule tells you when it needs testing.

When to see your vet

  • Any new lump, bump, scaly patch or sore on your cat [3][9]
  • A sore or crusty spot on the nose, ears, eyelids or lips of a white or partly white cat [8]
  • Red, thickened or scaly skin on those same sun-exposed areas [9]
  • A lump at a vaccination site that meets any part of the 3-2-1 rule [13]
  • A lump that has been removed before and seems to be coming back [8][11]

Some lumps in cats are not tumors at all. For raised sores and swellings caused by inflammation, see eosinophilic granuloma complex in cats.

FAQ

Are most lumps on cats cancer?
No single answer fits every lump. Skin and soft tissue growths in cats include a fair share of benign ones, but cancers such as sarcomas and squamous cell carcinomas are common too, so any lump should be checked by a vet. [1][3]

Should a benign lump always be removed?
Not always. Your vet will weigh the type of growth, where it is, how big it is and your cat’s overall health before suggesting surgery or watching it.

Should I stop vaccinating my cat because of sarcoma risk?
The 2026 review describes the tumor as rare and says its findings reinforce the importance of routine vaccination. Talk to your vet about which vaccines suit your cat. [12]

The bottom line

Skin and soft tissue growths are among the most common tumors in cats, and they can look like lumps, scaly patches or sores. Only a vet’s tests can say whether a growth is benign or cancerous. White or partly white cats are at higher risk of sun-related squamous cell carcinoma on the nose, ears, eyelids and lips, and any lump at a vaccination site should be checked against the 3-2-1 rule.

This article is for general information and is not a substitute for veterinary advice. If you find a lump or a sore that will not heal on your cat, please see your veterinarian.

Sources

  1. Brilhante-Simões P, Lopes R, Delgado L, et al. Mapping Feline Oncology in Portugal: A National Characterization. Animals. 2026;16(3):364. doi:10.3390/ani16030364 (CC BY 4.0). https://pmc.ncbi.nlm.nih.gov/articles/PMC12897375/
  2. Giuliano A, Horta RDS, Engel LS, et al. Cancer Across Domestic Animals: A Descriptive Review from the Veterinarian’s Perspective. Veterinary Sciences. 2026;13(2):167. doi:10.3390/vetsci13020167 (CC BY 4.0). https://pmc.ncbi.nlm.nih.gov/articles/PMC12944839/
  3. 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/
  4. Vincenti S, Aeschlimann L, Brunner A, et al. Combined cross-sectional and tangential margin evaluation of different tumor types in dogs and cats. Frontiers in Veterinary Science. 2025;12:1629994. doi:10.3389/fvets.2025.1629994 (CC BY). https://pmc.ncbi.nlm.nih.gov/articles/PMC12580621/
  5. Juodžiukynienė N. Retrospective Analysis of Prevalence of Tumors in Dogs and Cats in Lithuania. Veterinary Sciences. 2025;12(11):1038. doi:10.3390/vetsci12111038 (CC BY 4.0). https://pmc.ncbi.nlm.nih.gov/articles/PMC12656924/
  6. 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, With a Short Literature Review of Feline, Equine, and Human Proliferative Mast Cell Disorders. Veterinary Sciences. 2026;13(5):500. doi:10.3390/vetsci13050500 (CC BY 4.0). https://pmc.ncbi.nlm.nih.gov/articles/PMC13211724/
  7. Melville K, Smith KC, Dobromylskyj MJ. Feline cutaneous mast cell tumours: a UK-based study comparing signalment and histological features with long-term outcomes. J Feline Med Surg. 2015;17(6):486-493. PMID 25193279. https://pubmed.ncbi.nlm.nih.gov/25193279/
  8. Linhares LCM, Rangel MMM, de Oliveira KD, et al. Prognostic significance of EGFR-1 and VEGF-A expression in feline cutaneous squamous cell carcinoma. Frontiers in Veterinary Science. 2026;13:1949867. doi:10.3389/fvets.2026.1949867 (CC BY). https://pmc.ncbi.nlm.nih.gov/articles/PMC13711497/
  9. Granados-Soler JL, Story MM, Allavena R. Ultraviolet Light-Induced Skin Cancer and the Safety of Sunscreen Use in Pets: An Important but Under Researched Aspect of Companion Animal Health. Veterinary Sciences. 2026;13(7):605. doi:10.3390/vetsci13070605 (CC BY 4.0). https://pmc.ncbi.nlm.nih.gov/articles/PMC13416697/
  10. Cappelleri A, Brambilla E, Chiti LE, et al. Expression of αv Integrin in Feline Injection-Site Sarcoma (FISS): Preliminary Investigations. Animals. 2024;14(24):3588. doi:10.3390/ani14243588 (CC BY 4.0). https://pmc.ncbi.nlm.nih.gov/articles/PMC11672646/
  11. Wojtkowska A, Małek A, Giziński S, et al. Comparison of MMP-2, MMP-9, COX-2, and PGP Expression in Feline Injection-Site and Feline Noninjection-Site Sarcomas: Pilot Study. Animals. 2024;14(14):2110. doi:10.3390/ani14142110 (CC BY 4.0). https://pmc.ncbi.nlm.nih.gov/articles/PMC11273489/
  12. Emdin F, Naro SG, Hoang PM, Brown KA, Daneman N, Weese JS. The incidence of vaccine-associated sarcomas in cats: a systematic review and meta-analysis. J Small Anim Pract. 2026 (online ahead of print). PMID 42532508. https://pubmed.ncbi.nlm.nih.gov/42532508/
  13. AAHA/AAFP. 2020 AAHA/AAFP Feline Vaccination Guidelines: Adverse Postvaccination Reactions. American Animal Hospital Association (published Aug 13, 2020). https://www.aaha.org/aaha-guidelines/2020-aahaaafp-feline-vaccination-guidelines/adverse-postvaccination-reactions/ (read via https://web.archive.org/web/20240806103210/https://www.aaha.org/aaha-guidelines/2020-aahaaafp-feline-vaccination-guidelines/adverse-postvaccination-reactions/). Journal version: Stone AE, et al. J Feline Med Surg. 2020;22(9):813-830. PMID 32845224.