Squamous Cell Carcinoma

Squamous Cell Carcinoma


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Basic Information image



Definition


Squamous cell carcinoma (SCC) is a malignant tumor of epithelial cell origin, specifically keratinocytes. SCC is the most common neoplasm of the equine eye and ocular adnexa and the second most common tumor of horses overall.



Epidemiology



Species, Age, Sex




• The mean age at diagnosis is approximately 11 years, but a range of 3 to 26 years is reported.


• The gender predisposition of SCC is not well understood. Geldings have been overrepresented in selected studies. However, this finding may simply reflect gender distribution of the general client-owned equine population.



Genetics/Breed Predisposition/Risk Factors




• An increased prevalence of SCC is associated with various environmental factors, including geographic influences of increased longitude, decreased latitude, increased altitude, and increased mean annual solar radiation exposure.


• A breed predilection exists for Draft horses, Appaloosas, and Paint horses.



Contagion and Zoonosis


SCC is not believed to be contagious. There has been one case report of penile SCC identified bovine papillomavirus within SCC tumor nuclei. Current studies are investigating a viral cause in ocular SCC.



Geography and Seasonality


Irritation from actinic or ultraviolet (UV) radiation has been thought to promote the development of SCC. Clinically, horses living at higher elevations with increased sunlight exposure have a higher incidence of SCC.



Associated Conditions and Disorders


Any chronic irritation may promote neoplastic transformation of epithelium into SCC, especially at mucocutaneous junctions (see Etiology and Pathophysiology below).



Clinical Presentation


SCC frequently affects the skin, external genitalia (eg, penis; most commonly the glans penis followed by the urethra), nasal and paranasal sinus (especially the caudal maxillary sinus), and eye and periocular areas. Case reports or small case series exist of SCC in many sites such as the hoof wall, thyroid gland, and stomach. Ophthalmic presentations of SCC vary and may involve the corneoconjunctiva, bulbar conjunctiva, third eyelid, and eyelids. The biologic behavior of ocular SCC is reported to differ depending on the location, with the prognosis for eyelid SCC worse compared with other sites of the eye.



History, Chief Complaint




• Suspect SCC with any erosive, erythematous, or raised mass


• Hematospermia for tumors of the glans penis


• Signs referable to paraneoplastic syndromes


image Hypercalcemia of malignancy (often described as pseudohyperparathyroidism)

image Hypertrophic osteopathy (a painful condition of the long bones) has been reported with primary and metastatic pulmonary SCC.

• Signs referable to the location of the tumor


image Tumors of the nasal or paranasal sinuses: Unilateral purulent or mucopurulent nasal discharge with or without epistaxis

image Tumors of external genitalia or bladder: Hematuria, dysuria, urine retention with possible bladder rupture, and reproductive dysfunction

image Tumors of the esophagus or stomach: Weight loss, dysphagia, anorexia, anemia (normochromic and normocytic), neutrophilia, carcinomatosis with peritoneal effusion, high metastatic rate

image Disseminated thoracic SCC: Exercise intolerance, increased respiratory rate and effort at rest, pleural effusion, poor performance, weight loss, inappetence

image Periocular or ocular SCC: Mucopurulent discharge, blepharospasm, tan to reddish raised nodular mass, or erosive plaques


Physical Exam Findings


Regardless of the location, the most common physical examination finding is a hairless, friable, proliferative mass lesion. Regional lymphadenopathy may be detected in 15% of cases or fewer. Masses often bleed easily with manipulation.



Etiology and Pathophysiology




• SCC has been reported to develop in chronic wounds, at burn sites, and at sites of epithelial scarring (ie, locations consistent with chronic inflammation and prolonged wound healing).


• UV light exposure (with accompanying solar elastosis)


• Overexpression of the tumor suppressor protein p53, possibly mutated because of UV radiation, plays an important role in SCC development in many animals. In two separate studies, 100% of equine ocular SCCs overexpressed p53.


• Cyclooxygenase (COX) enzyme overexpression


image High levels of COX-2 expression have been detected in many human and veterinary neoplasms, including SCC of the head and neck.

image Correlations have been made in humans with head and neck SCC between overexpression of COX-2 in neoplastic tissues and poor prognostic factors.

image A limited number of investigations specifically examining the role of COX in naturally occurring equine ocular and periocular SCC have been conducted to date, and the role of COX expression in the etiopathogenesis of SCC is as yet undetermined.


Diagnosis image



Differential Diagnosis




• Other tumors (papilloma, melanoma, mastocytoma, basal cell carcinoma, schwannoma, adenoma and adenocarcinoma, hemangioma and hemangiosarcoma, lymphoma and lymphosarcoma), inflammatory lesions (abscesses, granulation tissue, foreign body reaction, solar-induced inflammation, dermatitis, eosinophilic dermatitis, and botryomycosis)


• Affected nasal and paranasal cavities should have other primary tumors (sarcomas), as well as non-neoplastic processes such as maxillary (sinus) cysts, progressive ethmoid hematoma, and inflammatory polyps ruled out.


• Additional differentials to be considered when presented with ocular SCC include other causes of conjunctivitis (lymphoid hyperplasia and follicular conjunctivitis) and parasitic infections (Habronema, onchocerca, Thelazia).

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Jul 24, 2016 | Posted by in SMALL ANIMAL | Comments Off on Squamous Cell Carcinoma

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