Neoplastic Conditions

Actinic keratosis

These lesions are often associated with chronic sun exposure, so are generally seen in pale-skinned areas of animals with outside access. Lesions may be single or multifocal, and plaquelike or papillomatous with hyperkeratosis. They may progress to squamous cell carcinoma which has the potential for local invasion and distant metastasis.

Adrenocortical tumour

Adrenocortical tumours are responsible for 15-20% of hyperadrenocorticism cases in the dog, and 20% in the cat (see under Endocrine conditions). They are usually unilateral (although 10% of cases have bilateral tumours) and may be adenomas or carcinomas. The latter may be invasive and metastasise.

Anal sac adenocarcinoma

Anal sac adenocarcinoma is a malignant tumour which is palpable as a discrete or infiltrative mass in the anal sac. These tumours are often associated with hypercalcaemia and metastasise early to the sublumbar lymph nodes, spleen and lung. They are rare in the cat.

Anaplastic sarcoma

A poorly-differentiated malignant soft-tissue tumour derived from the mesenchymal connective tissues of the body.

Basal cell tumour

These common skin tumours arise from the basal epithelial cells which give rise to the epidermis. They are usually well-circumscribed, firm, freely-mobile masses found in the dermis and subcutis around the head and neck. They are generally slow-growing and benign in behaviour, rarely metastasising.

Benign fibrous histiocytoma

These rare skin tumours may be reactive proliferations rather than true neoplasias. Lesions can be solitary or multiple and predilection sites include the face, legs and scrotum.

Canine anterior uveal melanoma

See under Ocular conditions.

Canine cutaneous histiocytoma

These skin tumours are commonly seen in young dogs, and appear as solitary, firm, well-circumscribed intradermal nodules on the head, limbs or trunk. Occasionally the surface will ulcerate. They are benign and most will regress spontaneously over a period of months.


Chemodectomas are derived from the chemoreceptor cells of the aortic and carotid bodies which detect changes in the blood pH, oxygen and carbon dioxide levels. Chemodectoma of the aortic body arises at the heart base and is reported more frequently than carotid body tumours which arise at the bifurcation of the carotid artery and present as a cervical mass. Both are relatively uncommon in the dog and cat, but brachycephalic dogs appear predisposed. Chemodectomas may be locally invasive and have the potential to metastasise.


This is the second most common primary bone tumour of dogs accounting for 5-10% of cases. It is generally slower growing and metastasises less frequently than the osteosarcoma.

Colorectal cancer

Intestinal canacer is not common in the dog or cat. In the dog, cancer of the large intestine is more common than that of the small intestine, adenocarcinoma/carcinoma being the most common malignant tumour. In cats most tumours arise in the small intestine.

Cutaneous papillomas

These are pedunculated or vegetative skin growths found in older dogs and are distinct from the virally-induced papillomas found on the mucous membranes of young dogs. They are considered benign.

Cutaneous plasmacytoma

These neoplasms are derived from plasma cells. They occur commonly on the digits, the lips, the chin and the ear canal.

Fibromatous epulis

A common oral tumour of the dog presenting as a firm gingival mass. These tumours are benign, neither invading locally nor metastasising.


These are uncommon benign neoplasms. They are usually solitary, well-circumscribed lesions.


A fibrosarcoma is a malignant tumour derived from fibrous tissues and may be found in many sites including the bone, skin, spleen and oral cavity. Tumour behaviour varies with the site and histological grade. In general, fibrosarcomas are locally invasive but have a relatively low rate of metastasis (25% has been suggested for oral fibrosarcoma).


Haemangiomas are benign tumours arising from the vascular endothelial cells of the dermis and subcutis. They are common in dogs but rare in cats. They appear as well-circumscribed blue/purple masses.


This is a highly malignant tumour arising from vascular endothelial cells. Primary sites include the right atrium of the heart, spleen, liver, skin, bone, nervous system, kidney, bladder and oral cavity. Metastasis to a wide variety of sites is common, in many cases micrometastasis having occurred by the time of diagnosis.


These common tumours are derived from vascular pericytes. They are usually well-circumscribed and are often found on the limbs. Metastasis is rare, but they frequently recur locally, so treatment of choice is wide surgical excision or amputation.


A disorder of histiocytes which takes two forms, both relatively rare. In Malignant histiocytosis, proliferation of histiocytes results in solid tumour masses in a variety of organs including the spleen, liver, lymph nodes and lung. The disease is rapidly progressive and fatal. It has been most commonly reported in the Bernese Mountain Dog, but occasionally in other breeds. Systemic histiocytosis follows a more chronic, fluctuating course and involves the skin, eyes and peripheral lymph nodes. Systemic histiocytosis has only been reported in the Bernese Mountain Dog and is more often seen in younger dogs than the malignant form.


See under Endocrine conditions.

Intestinal adenocarcinoma

See under Gastrointestinal conditions.


Also known as intracutaneous cornifying epithelioma. These benign cutaneous neoplasms can be solitary or multiple.

Limbal melanoma

See under Ocular conditions.


Benign tumours of fat cells which are generally found in the subcutaneous tissues. They are common, affecting up to 16% of dogs. Infiltrative lipomas are locally invasive making surgical excision more difficult, but they do not metastasise.


These rare malignant tumours arise from the subcutaneous lipoblasts. These tumours are infiltrative but rarely metastasise.


Lymphosarcoma is a malignant lymphoproliferative disease also commonly termed malignant lymphoma. Lymphosarcoma is the most common haematopoietic tumour in the dog and cat. Lymphosarcoma may be classified anatomically by the location of the disease (multicentric, mediastinal, alimentary, cutaneous or extranodal), histologically or immunophenotypically as B-cell or T-cell.

Malignant histiocytosis

See Histiocytosis.

Mammary tumours

These are common in both the dog and the cat. Mammary tumours are derived from the epithelial and sometimes myoepithelial tissues of the mammary glands. In dogs approximately 50% are benign, in cats over 80% are malignant. Entire animals or those spayed after several seasons are predisposed. Behaviour varies depending on the histological grade, but malignant mammary tumours may be very aggressive, metastasising to the local lymph nodes, lungs and occasionally the abdominal organs and bone.

Mast cell tumours

Mast cell tumours are relatively common in dogs, representing up to 20% of skin tumours. They may present in a wide variety of forms so need to be included in the differential of all skin masses. Behaviour varies from benign to highly-aggressive malignant tumours which have the potential to metastasise (usually to the liver, spleen or kidney). Cutaneous mast cell tumours are less common in the cat, but systemic and intestinal forms of mast cell tumour may also be seen in this species.


Melanomas represent 4-6% of canine skin tumours and 1-2% of all feline skin tumours. They present as firm, pigmented dermal masses and are more common in dark-skinned dogs. Those found on the digits and close to mucocu-taneous junctions tend to be more malignant and may metastasise to local lymph nodes, lungs and other more distant sites.


These rare neoplasms arise from fibroblasts and occur more frequently on the limbs, dorsum or inguinal regions. Myxomas are benign and myxosarcomas are malignant.

Nasal cavity tumours

The most common nasal cavity tumours diagnosed in the dog are carcinomas (in particular adenocarcinomas). Other types include sarcomas (fibrosarcoma, chondrosarcoma or osteosarcoma), lymphoma and melanoma. Most are malignant, causing local invasion and progressive destruction, but are slow to metastasise. Dolichocephalic dogs, particularly of large and medium size, are reported to be at increased risk. In the cat, adenocarcinoma is the most common tumour followed by lymphoma.

Non-epitheliotropic lymphoma

This uncommon neoplasia is a form of cutaneous lymphosarcoma. It is usually generalised or multifocal. Nodules are seen in the dermis, and spread to the lymph nodes and internal organs may occur.


Osteosarcoma is the most common of the malignant primary bone tumours in the dog. It is rapid in growth and highly invasive and destructive. Osteosarcoma of the appendicular skeleton of dogs is highly malignant and metastasises early (commonly to the lungs). In common with other primary bone tumours, appendicular osteosarcoma is more common in large- and giant-breed dogs. Osteosarcoma of the axial skeleton (including the skull) is generally considered less malignant. Osteosarcoma in the cat is also less aggressive. See also under Musculoskeletal conditions.

Pancreatic carcinoma

A tumour of the duct cells of the pancreas. Uncommon, but usually highly malignant.

Parathyroid tumours

Parathyroid tumours are uncommon in the dog and cat. Functional adenomas are the most common type of parathyroid tumour resulting in primary hyperparathyroidism and hypercalcaemia (see Primary hyperparathyoidism under Endocrine conditions). Adenomas are benign and well-encapsulated. Adenocarcinomas may invade locally and metastasise.

Perianal (hepatoid) gland adenoma

These are benign tumours that arise from the modified sebaceous glands of the perianal area. They appear as well-circumscribed raised lesions which may ulcerate. Perianal gland adenocarcino-mas may occur, but are less common.


See under Endocrine conditions.


A rare benign tumour of the hair follicle. Pilomatricoma presents as a solitary, firm mass in the dermis or subcutis, without ulceration of the overlying epidermis. They usually occur over the back and limbs of dogs. They are rare in cats.

Pituitary tumours

The most common pituitary tumour in the dog is the adenoma of the corticotrophic cells of the anterior lobe. These tumours are generally functional, resulting in an overproduction of adrenocorticotrophic hormone (ACTH) and hyperadrenocorticism (see under Endocrine conditions). Carcinomas do occur and are generally non-functional but are more invasive and likely to metastasise. In the cat, pituitary tumours may be associated with hyperadrenocorticism as above, but tumours of the somatotrophic cells of the anterior pituitary also occur resulting in an overproduction of growth hormone and acromegaly.

Primary bone tumours

Primary bone tumours are relatively uncommon in the dog and represent <5% of all tumours. The most common tumours are osteosarcomas and chondrosarcomas, others, including fibrosarcomas and haemangiosarcomas, occur less frequently. In dogs, the risk of primary bone tumours of the appendicular skeleton increases with body size/weight. They generally occur in older dogs, but in giant breeds they may be seen at an earlier age. Primary bone tumours are uncommon in the cat. See also Osteosarcoma and Fibrosarcoma.

Primary brain tumours

See under Neurological conditions.

Renal cystadenocarcinoma

See under Renal and Urinary conditions.


This rare neoplasm arises from the Schwann cells of the nerve sheath and can be dermal or subcutaneous. In dogs they occur most commonly on the limbs, head and tail. They are often alopecic and occasionally pruritic or painful.

Sebaceous gland tumours

One of the most common skin tumours of the dog, but less common in the cat. They may be single or multiple. There are various his-tologic types: sebaceous hyperplasia presents as small, lobulated wart-like lesions; sebaceous epitheliomas present as firm dermal masses with hairless overlying skin. Other types include sebaceous gland adenomas and adenocarcinomas. With the exception of adenocarcinomas, sebaceous gland tumours are generally benign in behaviour.

Squamous cell carcinoma of the skin

These are relatively common malignant tumours which arise from keratinocytes. Various predisposing factors have been identified, such as exposure to ultraviolet light, pollutants and pre-existing chronic dermatitis.

Squamous cell carcinoma of the digit

Squamous cell carcinoma is the most common cutaneous tumour of the digit in dogs. It is locally invasive, resulting in bone lysis, and metastasises more frequently than squamous cell carcinomas found in other cutaneous sites.

Sweat gland tumours

These may be adenomas or adenocarcinomas. They are uncommon in the dog and rare in the cat. They may present as small solitary nodules in the dermis and subcutis with or without ulceration. An inflammatory form of adenocarcinoma is poorly circumscribed and more infiltrative. Adenocarcinomas are highly invasive and may metastasise to local and regional lymph nodes, and occasionally to more distant sites, e.g. the lungs.

Systemic histiocytosis

See Histiocytosis.

Testicular neoplasia

Testicular neoplasia is common in the dog. There are three main tumour types: Sertoli cell tumours, seminomas and interstitial cell tumours. Certain breeds seem at increased risk. The incidence of Sertoli cell tumour and seminoma is higher in undescended testes than normally descended testes.


Thymoma is a tumour of the epithelial cells of the thymus gland which is situated in the cranial mediastinum. It is uncommon in both dogs and cats. Thymomas are generally benign and slow growing. Symptoms relate to the presence of a cranial mediastinal mass and may vary: cough, dyspnoea, regurgitation and occasionally obstruction of the cranial vena cava leading to facial and forelimb oedema (‘precaval syndrome’). Autoimmune conditions such as Myasthenia gravis may be associated with thymoma.

Thyroid Carcinoma

See Thyroid neoplasia in dogs under Endocrine conditions.


These are common benign skin tumours, appearing as solitary, domed masses. They may become dark in colour and ulcerate.


A benign tumour of the hair follicle. They present as solitary, firm masses in the dermis or subcutis, often with ulceration of the overlying epidermis. They usually occur over the back and limbs of dogs, but are rare in cats.


This rare, benign tumour occurs most commonly on the head and neck.