Introduction

Skin tumours are a common reason why patients are presented to clinics as they are easily seen by the owner. Initially tumours need to be differentiated from inflammatory lesions, cysts and haematomas.

As the skin has multiple functions, tumours can arise from many different cells. In dogs about two-thirds of tumours of the skin and subcutis are benign and one-third are malignant. In cats two-thirds are malignant and one third benign.

Identifying skin tumours and deciding whether to remove them is an important part of small animal practice.

Dogs

Papilloma (Wart)

Papillomas are virally induced benign tumours of the skin. They are usually small, solitary, superficial and pedunculated lumps that are hard. They may bleed after trauma. They are usually ignored but can be surgically removed.

Lipoma

Lipomas are benign tumours of fat. They are variable in size and shape, slow growing and can appear anywhere and are usually soft and subcutaneous. They are diagnosed on fine needle aspirate and have a greasy appearance. Treatment is usually not necessary unless they interfere with mobility or are rapidly growing.

Soft Tissue Sarcomas

These are named according to their histological appearance but largely behave the same. They are often solitary, variable in size, firm and poorly circumscribed. They can be difficult to diagnose from a fine needle aspirate as they exfoliate poorly. Only a few will metastasise but local recurrence is a problem if wide surgical margins cannot be obtained. Radiotherapy can be used postoperatively on limbs.

Mast Cell Tumours

These are the great pretenders and have a variable appearance. A diagnosis can be made on fine needle aspirate. This enables an appropriate treatment plan to be formulated. These tumours are graded from low to high. The low-grade tumours can be removed with wide surgical excision including deep margins. The high-grade tumours have a poorer prognosis and are likely to spread. The local lymph node needs to be palpated and a fine needle aspirate taken. Other tests may be required if the tumour is a higher grade.

Histiocytoma

Histiocytomas are mainly tumours of young dogs. They tend to develop rapidly, are dome shaped, without hair and can ulcerate. Although they are rapidly growing they are benign and are unusual as they spontaneously regress and therefore do not require any treatment.

Squamous Cell Carcinoma

These are firm nodular masses which may be raised or erosive. Sites exposed to the sun are most at risk. They usually involve the limbs and can be ulcerated and bleed. The majority have a good prognosis with wide surgical excision. They rarely metastasise to the lymph nodes and lungs. The exception to this is digital SCC, which tends to be more aggressive; however, they can go on for years, in which case the digit needs to be amputated.

Melanoma

These can vary in presentation from flat pigmented areas to raised nodules. Most skin melanomas are benign except for the ones on the digit. Oral melanomas are malignant. The local lymph node should be palpated and chest radiographs taken if the digit is involved. Treatment is with wide surgical excision. There is no treatment for metastatic disease.

Cystic Tumours

Most of these are benign. When ruptured they can set up a marked inflammatory reaction requiring surgical excision.

Sebaceous Gland Tumours

These are often misdiagnosed as sebaceous cysts. These tumours can range from benign to malignant. The latter grow more rapidly and metastasise. For benign lesions surgery should be curative.

Cats

Squamous Cell Carcinoma

These are most common around the head, especially the ears, nose and eyelids, where the skin is often not pigmented or poorly haired and exposed to the sun. They usually progress slowly starting as erythematous lesions with a waxy scab. Over time these can become ulcerated. They rarely metastasise. Various treatments are available including surgery, radiotherapy and photodynamic therapy.

Basal Cell Tumours

This is the most common skin tumour in middle-aged to older cats. They are benign tumours, usually found on the head and neck, well demarcated, small and firm. Surgery is the treatment of choice.

Summary

Skin tumours are common but vary in their behaviour from benign to malignant. Therefore it is important to make a diagnosis either via a fine needle aspirate or biopsy to formulate an appropriate treatment plan and to advise owners on prognosis.

References

1.  Brearley M. Epithelial and other solitary skin tumors. In: Dobson, JM; Lascelles BDX. eds. BSAVA manual of canine and feline oncology (second edition). Gloucester: BSAVA, 2003; 152-160.

2.  Ogilvie G, Moore A. Tumors of the skin and surrounding structures. In: Ogilvie, G; Moore, A. eds. The veterinary cancer patient: a practice manual. New Jersey: Veterinary Learning Systems, 1996; 473-502.

3.  Vail D, Withrow S. Tumors of the skin and subcutaneous tissues. In: Withrow and MacEwens's small animal clinical oncology. Canada: Saunders Elsevier, 2001; 375-401.