Squamous Cell Carcinoma
Introduction
Squamous cell carcinomas are the malignant equivalent of the papilloma and may arise anywhere within the oropharynx. These tumours are formed from epidermal cells with varying degrees of squamous cell differentiation. They are common in the cat, dog, horse and cow but can occur in other species. They are most likely to develop in non-pigmented areas of the skin as there is a known association between their development and exposure to UV light.
There are two forms of the neoplasm:
- Proliferative — cauliflower-like lesions
- Ulcerative — ulcerative lesions
The tumours are normally slow to metastasize but may be locally invasive.
Cat
Cutaneous squamous cell carcinomas are common in white cats, especially on the tips of the pinnae, nasal planum and eyelid. Multiple tumours may develop simultaneously as the tissue has been exposed to the same level of ultraviolet damage. Often the appearance of acinitic keratosis precedes the appearance of the tumour. The lesions are normally crusted, ulcerative and progress over time. They may begin very small and they are commonly mistaken for cat scratches, therefore it is essential that any 'scratch' that fail to heal is treated with suspicion and biopsied. Ideal treatment is radical excision. In the case of pinna SCC's, pinnectomy is indicated.
SCC of the nasal cavity are reported. These normally originate from the nasal vestibule and cause clinical signs associated with airway obstruction and tissue necrosis.
Squamous cell carcinomas of the oesophagus are most notably seen in the cat, where the tumour tends to infiltrate around the oesophageal wall resulting in a “ring carcinoma”. The affected cat has progressive difficulty in eating and swallowing. Oesophageal SCC forms part of upper alimentary tract carcinoma complex.
Dog
Cutaneous SCC's are common in white breeds of dog such as the Boxer, Dalmation and English Bull Terrier.
Horse
Cutaneous SCC's are the second most common neoplasms in the horse. Contact with penile smegma is thought to be an additional predisposing cause. They are most commonly located in the penile or clitoral regions and on non-pigmented skin. Lesions are progressive and potentially locally invasive. They may be ulcerative or proliferative and secondary infection is often present, producing a foul odour. Complete surgical excision is the gold standard treatment, but adjuncts may be required. Masses located around the eye may need prompt specialist treatment to save the eye.
SCC of the stomach is the most common gastric tumour in the horse. It has the appearance of a large cauliflower-like mass and affects the pars oesophagea. It metastasises and spreads and transcoelomically.
Rarely SCC can form in the nasal cavity of the horse. These originate from the maxillary sinus and cause facial distortion, tissue necrosis and airway obstruction. A serosanginous or mucopurulent, odorous nasal discharge may be present.
Cow
As mentioned, squamous cell carcinomas are most likely to develop on non-pigmented areas of skin such as the eyelids. Additionally, there is thought to be an association between the ingestion of bracken fern carcinogens and the malignant transformation of papillomas to squamous cell carcinomas in cattle.
Squamous cell carcinomas of the oropharynx in cattle are commonly seen as part of an upper alimentary tract carcinoma complex.
Diagnosis
FNA's can be performed as a first line diagnostic. Cytology may show:
- Pleomorphic epithelial cells - these have a variable appearance from benign keratinized mature squames to epithelial cells with anisocytosis, basophilic cytoplasm and extensive vacuolation.
- Binucleate cells, chromatin clumping and prominent nucleoli may be present
Any mass suspicious of squamous cell carcinoma should be biopsied to confirm diagnosis.
Histopathological examination of a biopsy of the mass should reveal:
- Irregular cords or masses of epidermal cells entering the dermis
- Keratin pearls
- High mitotic rate
- Large nuclei with prominent nucleoli
- Central necrosis accompanied by high neutrophil numbers
Treatment
Dependant on the site of neoplasia, treatment may involve debaulking/complete excisional surgery, radiotherapy, cryosurgery, photodynamic therapy and hyperthermia. However complete surgical excision is the ideal.
Although the metastatic rate of these tumours is normally slow, screening should be performed prior to the start of treatment. This involves radiography of the thorax and fine needle aspiration of local lymph nodes.
Prognosis
The smaller the tumour is identification, the better the chance of successful removal and a good prognosis. As mentioned, these tumours are often locally invasive but slow to metastasise, however the level of malignancy and therefore prognosis is often related to the location of the neoplasm. Those arising over the tonsil (squamous carcinoma of the tonsil or tonsillar carcinoma) are very malignant, invading adjacent tissues and metastasising early. Squamous carcinomas of the tongue (especially in cats) can also behave in a very malignant fashion. Those at more rostral sites, e.g. on the incisor gingivae, are less likely to metastasize early although they may be locally aggressive. They should be staged according to the World Health Organisation (WHO) system.
Prevention
Squamous cell carcinomas can be prevented by protecting the skin from ultraviolet light. This may be achieved using sunblocks or by keeping the animals indoors or in the shade. This is rarely practicable.
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Cytology Q&A 14 |
References
Bond, Hendricks, Loeffler (2009) Veterinary Dermatology RVC Intergrated BVetMed Course, Royal Veterinary College
Freeman, KP (2007) Self-Assessment Colour Review of Veterinary Cytology - Dog, Cat, Horse and Cow Manson
Murphy, S (2006) Skin neoplasia in small animals 1. Principles of diagnosis and management In Practice 2006 28: 266-27
Murphy, S (2006) Skin neoplasia in small animals 2. Common feline tumours In Practice 2006 28: 320-32
Quinn, G (2003) Skin tumours in the horse: clinical presentation and management In Practice 2003 25: 476-48