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, what were called basal cell tumours are now classified as trichoblastomas — 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 and, when it does, may spread to lymph nodes and other organs. Owners typically notice a small, firm, often hairless lump on the skin, most commonly on the head, neck, or limbs. 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 — which 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, with a typical age around seven years. 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. Certain breeds may be more likely to develop these growths — poodles, cocker spaniels, and some terrier breeds in dogs; long-haired breeds such as Persians and Himalayans in cats — though they can occur in any breed or in mixed-breed animals.
Most of these tumours grow slowly over weeks to months and remain localised to the skin. In dogs, trichoblastomas typically do not change in character once they have reached a certain size, and they do not spread to other parts of the body. In cats, the majority behave in a similarly quiet fashion, though the malignant form — basal cell carcinoma — can behave more aggressively, with the potential to invade deeper tissues and, in a small number of cases, spread to lymph nodes or internal organs. 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.
Location on head, neck, or limbs
These growths commonly appear on the head — particularly around the ears or face — the neck, or the upper parts of the legs. Owners often find them when handling these areas during petting 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
If a basal cell carcinoma is present and spreading, the lymph nodes that drain the area may become firm and swollen. This is more commonly observed in cats than in dogs and may be noticed under the jaw, in the armpit, or behind the knee, depending on the location of the original lump.
Multiple lumps appearing
Occasionally, more than one growth may develop over time, either in the same region or elsewhere on the body. Each lump represents a separate event rather than spread from the original site, particularly in benign forms.
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. Additional imaging may be considered if there is concern about spread, particularly in cats where malignant behaviour is possible.
Physical examination
Cytology
Histopathology
Abdominal ultrasound
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 for definitive 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. Cytology or clinical assessment may have already 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 provide a definitive 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 tumour could grow 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, clearly benign-appearing lesions and are less suitable for larger or deeper tumours or when there is any concern about malignancy.
Chemotherapy or radiation therapy
In cats with basal cell carcinoma that has spread to lymph nodes or other organs, or in cases where complete surgical removal is not possible, 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: These approaches require referral to a specialist centre, 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."
Most small skin lumps in dogs and cats are benign, but 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 or histopathology is needed to make that distinction, and 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, but basal cell carcinoma can recur locally if the margins are not clear, and in a small number of cases it may have already spread to lymph nodes or internal organs at the time of diagnosis, which affects the longer-term outlook.
"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 and carries a different prognosis.
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. Both conditions involve accumulation of specific cell types in the skin and typically require histopathology to confirm the underlying process.
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.
Alabama Rot (CRGV)
Acral lick dermatitis can produce a thickened, raised skin lesion that may be mistaken for a skin tumour such as a trichoblastoma on casual observation, particularly when the licking behaviour has gone unnoticed. The two are distinguished by history, location, and the appearance of the tissue under the microscope.
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 seen in basal cell tumour nomenclature.
If a lump has been found and removed, the histopathology report is the most useful 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: 12 September 2026 · Dr Alastair Greenway MRCVS