Basal cell tumors and hair follicle tumors are growths that start in the skin and the hair follicles, the small pockets that each hair grows from. A veterinary pathology review notes that, among domestic animals, hair follicle tumors turn up most often in dogs, and that most of them are benign, although malignant kinds also exist [1]. Benign means the tumor does not spread to other parts of the body.
A broad review of cancer in domestic animals adds that skin tumors of this epithelial type are common in both dogs and cats and are usually benign [4]. Only a lab exam of cells or tissue from the lump can tell which kind it is [1][2].
Any new lump on your pet should be checked by your vet. A lump cannot be judged safe by how it looks or feels. For other kinds of lumps, see lumps and bumps on dogs and lumps and bumps on cats.
Basal cell tumors
Pathologists sort these lumps by the part of the normal hair follicle that the tumor cells look like [1]. That is why a lab report on a lump that an older text might call a “basal cell tumor” may use a follicle name such as trichoblastoma instead. Ask your vet what the name on your pet’s report means.
In dogs:
- Who: in a study of 1,185 dog skin tumors from a lab in northern Portugal, trichoblastomas were seen mostly in older dogs (the middle age was about 9 years), and Cocker Spaniels and German Shepherds had them more often than other breeds in that group [2].
- Where: the same study found them mostly on the head, including the face, the top of the head and the ears [2].
- How common: they made up under 2% of the dog skin tumors in that study [2].
In cats:
- How common: in a national study of about 1,900 tumors in cats in Portugal, trichoblastoma was among the six most frequent tumors of the skin and soft tissue [3].
- Who: that study found no clear link between breed and tumor type, and cats with malignant tumors tended to be older than cats with benign ones [3].
- Look: a lump cannot be named by sight. The study’s authors advise that any new mass in a cat be checked promptly [3].
Some skin tumors in cats are dark, so they can look like other dark skin lumps. See skin melanoma in dogs and cats.
Hair follicle tumors
Hair follicle tumors are mainly a dog problem among domestic animals [1]. In the Portuguese dog study they made up about 6% of all skin tumors, and they included several kinds [2]. That study noted that these tumors often affect dogs with short, thick coats [2].
Trichoepitheliomas. These were the most frequent hair follicle tumors in the dog study [2].
- They often appeared at several places on the body at once [2].
- Mixed-breed dogs, Basset Hounds, Boxers and Golden Retrievers were among the dogs affected, and Basset Hounds had them more often than other breeds [2].
- The middle age of affected dogs in that study was about 7 years [2].
Pilomatricomas. These were uncommon in the dog study, with only a handful of cases among more than a thousand skin tumors [2].
Trichilemmomas. These were rare, with two cases in the same dog study [2].
Infundibular keratinizing acanthomas. In the dog study these were found mostly on the back, neck and hind legs, and German Shepherds were among the breeds most often affected [2]. A related form grows under the nail (subungual keratoacanthoma) [2].
For other cysts in the skin of dogs, see skin cysts in dogs.
Rare malignant forms
A few of these tumors have malignant forms.
- Malignant hair follicle tumors: the large majority of hair follicle tumors are benign, yet some are malignant [1].
- Basal cell carcinoma: this was rare in the dog study, at about half of one percent of skin tumors [2].
Only a lab test of the lump can tell a benign tumor from a malignant one [1][2].
How vets find out what a lump is
Vets assess skin tumors with cytology and histopathology [2]. Cytology looks at cells taken from the lump, often with a thin needle (a fine needle aspiration). Histopathology looks at a piece of tissue (a biopsy) or the whole removed lump under the microscope. Pathologists name hair follicle tumors by which part of the follicle the cells resemble [1].
How vets treat them
Surgery is the main treatment.
- Skin tumors in general: the Portuguese dog study notes that surgical removal is still the preferred treatment for most skin tumors, and that the choice depends on the tumor type, grade, stage and location [2].
- Benign epithelial skin tumors: these are usually benign in dogs and cats [4]. Your vet will tell you what the lab result means for your pet.
Your vet will decide whether and how to remove a lump.
At home, as directed by a vet:
- do not squeeze, pick or try to drain a lump;
- stop your pet from licking, scratching or biting a lump in the way your vet advises;
- note the size, place and date of every lump so you can show your vet any change;
- go back for every recheck.
Outlook
Outcomes vary between types:
- Most hair follicle tumors are benign [1].
- Trichoepitheliomas often appear at several sites in the same dog, especially in Basset Hounds, so new lumps can show up later [2].
- Cats in the Portuguese study sometimes had more than one tumor type over time, more often older cats [3].
- Malignant forms are rare, and their outlook depends on the type and on whether the tumor has spread; your vet will explain this if the lab finds one [1][2].
These are statements about groups of animals. They cannot predict how one pet will do. Your vet can explain what this means for your pet.
When to see your vet
See your vet if your dog or cat has:
- any new lump in or under the skin [3];
- a lump that grows, changes color or becomes a sore;
- a lump that oozes or drains;
- a lump your pet keeps licking, scratching or biting;
- a new lump after one was removed before [2].
FAQ
Is a basal cell tumor cancer?
Usually not. Most hair follicle tumors are benign [1], and epithelial skin tumors in dogs and cats are usually benign [4]. Malignant forms exist, so your vet will want the lump tested [1][2].
What is a trichoblastoma?
It is a hair follicle tumor named for the part of the follicle its cells resemble [1]. In dogs it is often found on the head [2], and in cats it is one of the more frequent skin tumors [3].
Can my dog get more of these lumps?
Yes, with some types. Trichoepitheliomas often appear at several sites, especially in Basset Hounds [2].
The bottom line
Basal cell tumors (often reported as trichoblastomas) and hair follicle tumors are skin lumps in dogs and cats. Most are benign, and malignant forms are uncommon. Some breeds are affected more often, and some types tend to show up at more than one site. Only a lab test of the lump can tell the types apart. Surgical removal is the usual treatment, so have your vet check any new or changing lump.
This article is for general information only and does not replace advice from your veterinarian. If your pet has a new lump, see your vet.
Sources
- Wiener DJ. Histologic features of hair follicle neoplasms and cysts in dogs and cats: a diagnostic guide. J Vet Diagn Invest. 2021;33(3):479-497. PubMed abstract. https://pubmed.ncbi.nlm.nih.gov/33666111/
- Martins, Canadas-Sousa, Mesquita, et al. Retrospective study of canine cutaneous tumors submitted to a diagnostic pathology laboratory in Northern Portugal (2014–2020). Canine Medicine and Genetics. 2022. CC BY 4.0. https://pmc.ncbi.nlm.nih.gov/articles/PMC8875941/
- Brilhante-Simões, Lopes, Delgado, et al. Mapping Feline Oncology in Portugal: A National Characterization. Animals. 2026;16(3):364. CC BY 4.0. https://pmc.ncbi.nlm.nih.gov/articles/PMC12897375/
- Giuliano, Horta, Engel, et al. Cancer Across Domestic Animals: A Descriptive Review from the Veterinarian’s Perspective. Veterinary Sciences. 2026;13(2):167. CC BY 4.0. https://pmc.ncbi.nlm.nih.gov/articles/PMC12944839/