CONDITION
Basal Cell Tumours in Dogs and Cats
Basal cell tumours is a historical term for a group of skin growths that were once thought to arise from a single cell type, but are now understood to be distinct tumours with different origins. In dogs, most of what were called basal cell tumours are now classified as trichoblastomas. These are benign growths that develop from cells in the hair follicle. In cats, most are either trichoblastomas or apocrine ductular adenomas, which originate from sweat gland structures. The vast majority of these growths in both species are benign and behave in a quiet way once removed, though in cats a malignant form, basal cell carcinoma, can occur. Even this form usually stays in the skin, and spread to lymph nodes or other organs has been reported only rarely. Owners typically notice a small, firm, often hairless lump on the skin. In dogs it is most often on the head, neck or forelimbs, and in cats it can appear almost anywhere on the body. The lump may have been present for weeks or months and may grow slowly. In many cases, the growth is discovered during grooming or routine handling. There is often little else to observe: no pain, no discharge, no change in behaviour. This can make it difficult to know whether the lump warrants further attention. This page explores what these lumps can look like when they first appear, what is happening in the skin to produce them, how they are investigated and identified, and what approaches exist for managing them. The focus is on helping you understand the range of possibilities, the shape of the diagnostic process, and the factors that influence how these growths are handled once they are found.
Why this matters now
These growths tend to appear in middle-aged to older animals. In dogs, trichoblastomas are most often diagnosed between four and ten years of age. In cats, the mean age tends to be slightly higher, around nine to ten years, though these tumours can occasionally be found in younger animals. In dogs, Poodles, Cocker Spaniels and some terrier breeds, including the Kerry Blue Terrier, appear to be over-represented. In cats, long-haired breeds were at higher risk in a review of 124 cats, and Persian and Himalayan cats are often named among the breeds most at risk. These growths can occur in any breed and in mixed-breed animals.
Most of these tumours grow slowly over weeks to months and remain localised to the skin. In dogs, trichoblastomas are benign and do not spread to other parts of the body. In cats, the majority behave in a similarly quiet fashion. Basal cell carcinoma, the malignant form, can extend locally and occasionally regrows after incomplete removal, but in published series spread to lymph nodes or internal organs has been very rare, and the outlook after complete removal is generally very good. The pace and pattern vary between individuals, and the appearance of the lump alone does not always indicate how it will behave.
Signals & patterns
Early signals
Small, firm skin lump
A discrete, raised nodule that feels solid under the skin, often noticed during grooming or stroking. The lump may be movable or feel attached to the surrounding tissue, and it is usually not painful to the touch.
Hairless or thinning patch
The skin over the lump may lose hair or appear smooth and slightly stretched. This can make the growth more visible, particularly on areas where the coat is normally dense.
Slow, steady enlargement
The lump may increase in size gradually over several weeks or months. Many owners describe noticing it first as something very small, then realising over time that it has become more prominent.
Typical sites on the body
In dogs these growths are most often on the head, especially around the base of the ears, the neck or the forelimbs. In cats they can appear almost anywhere on the body. Owners often find them during stroking, grooming or bathing.
No obvious discomfort or change
The animal typically shows no sign of pain, itching, or altered behaviour. The lump may be present for some time before it is noticed, simply because it does not cause any distress.
Later signals
Ulceration or surface changes
In some cases, particularly with malignant forms in cats, the surface of the lump may break down, forming a raw or weeping area. This can occur with trauma or as the tumour grows and outstrips its blood supply.
Enlargement of nearby lymph nodes
Swelling of the lymph nodes that drain the area is uncommon with these growths. Spread from a basal cell carcinoma has been described in only a few individual cats, and a swollen node near a lump can have other causes, such as inflammation around an ulcerated lump or a different tumour type. The cause cannot be judged by touch alone.
Multiple lumps appearing
Occasionally, more than one growth may develop over time, either in the same region or elsewhere on the body. A new lump is usually a separate growth rather than spread from the first one, but it is not necessarily the same type of tumour, and its appearance alone cannot show which it is.
Click to read about the biological mechanisms
How this is usually investigated
The investigation usually begins with a physical examination to assess the lump's size, texture, attachment to deeper tissues, and whether other lumps are present. From there, the focus shifts to obtaining cells or tissue for microscopic examination, since the appearance alone does not reliably distinguish benign from malignant forms or separate these growths from other skin tumours. Imaging is not usually part of the work-up, because spread from these growths is rare. It may be considered for a tumour that is recurrent, unusually invasive or in an atypical site.
Physical examination
Cytology
Histopathology
Radiography
Options & trade-offs
Management is usually shaped by the tumour's location, size, whether it is causing discomfort or cosmetic concern, and in cats, whether there is any suspicion of malignant behaviour. Most owners and clinicians favour removing the lump surgically, both to relieve any local effects and to obtain tissue that confirms the diagnosis. The approach taken depends on what the owner finds workable, what the tumour's behaviour suggests, and what the histopathology reveals.
Surgical excision
The lump is removed under general anaesthesia, typically with a margin of normal tissue around it to reduce the chance of leaving tumour cells behind. The tissue is then submitted for histopathology to confirm the diagnosis and assess whether the margins are clear. In most cases, particularly in dogs with trichoblastomas, complete removal is curative and no further treatment is needed.
Trade-offs: Surgery requires anaesthesia, which carries its own considerations in older animals or those with concurrent health conditions. In cats with basal cell carcinoma, wider margins may be needed, and repeat surgery or additional treatment may be discussed if the initial excision is incomplete or if spread is identified.
Monitoring without intervention
Some owners choose to observe a small, slow-growing lump that is not causing any discomfort or interference with normal activity, particularly if the animal is elderly or has health conditions that make anaesthesia less straightforward. This is usually considered once cytology has suggested a benign process, and the decision is made to watch for any change in size, texture, or behaviour over time.
Trade-offs: This avoids the risks and costs of surgery, but does not confirm the diagnosis unless tissue is eventually obtained. It may suit animals with a limited life expectancy or when the lump is in a location where removal would be complex, though it leaves open the possibility that the lump could grow, prove to be a different tumour type if it has not been sampled, or, in cats, prove to be malignant.
Cryotherapy or laser ablation
In some settings, small superficial tumours may be treated by freezing with liquid nitrogen or removal using a surgical laser. These methods can be effective for localised benign growths and may avoid the need for sutures or a large surgical wound.
Trade-offs: These techniques do not always provide tissue for histopathology, which means the diagnosis remains presumptive unless a biopsy is taken separately. They are generally reserved for small lesions that cytology suggests are benign, and are less suitable for larger or deeper tumours or when there is any concern about malignancy.
Chemotherapy or radiation therapy
In the uncommon situation where a basal cell carcinoma cannot be completely removed, or in the rare case where it has spread, chemotherapy or radiation therapy may be considered. These treatments aim to slow tumour growth or reduce the size of residual disease, though the response varies and the evidence base in cats is limited.
Trade-offs: Radiation therapy is available only at specialist centres, and both approaches involve multiple visits and carry their own side effects and costs. They are not curative in most cases and are typically discussed when surgery alone is not sufficient or when the tumour's behaviour suggests a higher risk of recurrence or progression.
Common misconceptions
"A small, slow-growing lump is always harmless and does not need to be checked."
In dogs, most skin lumps turn out to be benign. In cats, a higher proportion of skin tumours are malignant. Appearance and growth rate alone do not reliably distinguish benign trichoblastomas from other tumour types, including mast cell tumours or, in cats, basal cell carcinoma. Cytology can often make that distinction, and histopathology confirms it, particularly in cats. Earlier sampling can help avoid uncertainty later if the lump changes.
"If the lump is removed completely, it will never come back."
In dogs, trichoblastomas rarely recur after complete excision, and the prognosis is excellent. In cats, benign forms also tend not to recur if fully removed, and basal cell carcinoma can occasionally regrow locally if the margins are not clear. Spread to lymph nodes or internal organs has been reported only rarely, and the outlook after complete removal is generally very good.
"All basal cell tumours are the same in dogs and cats."
The term 'basal cell tumour' is now recognised to cover several distinct growths with different cell origins and behaviours. In dogs, the vast majority are trichoblastomas, which are benign and do not spread. In cats, the picture is more varied, with most being benign trichoblastomas or apocrine ductular adenomas, but a malignant form, basal cell carcinoma, does exist. Even so, in cats it usually behaves in a locally confined way, and complete removal is usually curative.
Related conditions
Cutaneous Histiocytosis
Cutaneous histiocytosis can appear as firm skin nodules that may be difficult to distinguish from trichoblastomas or other benign growths without biopsy, particularly when the lesions first appear on the head or limbs.
Cutaneous Lymphoma
Cutaneous lymphoma may present as solitary or multiple skin lumps that can resemble benign growths such as trichoblastomas, and histopathology is often needed to distinguish between them. The distinction matters because cutaneous lymphoma carries a different prognosis and management approach compared to the benign tumours historically grouped under the basal cell tumour label.
Fibrosarcoma in Dogs
Fibrosarcoma in dogs can present as a firm mass in the skin or subcutaneous tissue, and on initial examination may not be readily distinguishable from a trichoblastoma or other benign skin tumour. Biopsy is required to differentiate between the two, as fibrosarcomas tend to behave in a locally invasive way while trichoblastomas are typically benign.
Dermatophytosis (Ringworm)
Dermatophytosis can occasionally produce focal areas of hair loss with thickened or crusted skin that may raise concern for a skin tumour, particularly in cats where fungal lesions can sometimes be nodular. Microscopy and fungal culture help distinguish the infectious process from the benign growths described on this page.
Acral Lick Dermatitis
Acral lick dermatitis can produce a firm, raised, hairless and sometimes raw area, usually on the lower part of a leg, that may resemble a skin tumour when the licking has gone unnoticed. The history of licking, the position of the lesion and the appearance of the tissue under the microscope help tell the two apart.
If a lump has been found and removed, the histopathology report is a key piece of information to have on hand, as it shapes what, if anything, might be discussed next. In cats, particularly those with a confirmed carcinoma, monitoring the regional lymph nodes and being aware of any new lumps can be part of the ongoing picture. Understanding how skin tumours in general are approached, and how they fit into the broader pattern of ageing in dogs and cats, can help frame these findings in a wider context.
Last reviewed: 9 October 2026 · Dr Alastair Greenway MRCVS