Introduction

The squamous cell carcinoma (SCC) is the most common skin tumor in cats, and it is related to the ultraviolet light exposure and local climate. The nose, eyelids and ears, especially of white cats, are more commonly affected (Carpenter et al. 1987, Moore & Ogilvie 2001, Ruslander 1997). This neoplasm affects mainly senior cats with a mean age of 12 years old and there is no sex or breed predilection (Rosychuk & Luttgen 1995). Squamous cell carcinomas are thought to be rapidly dividing tumors (Schwyn et al 1998). Macroscopically, the lesions begin with erythema, scales and crust formation (Hargis 1990). The evolution of the lesion will provoke corrosive ulceration, hemorrhage and pain (Muller et al, 1985a). The diagnosis is based on the clinical history, physical exam, and skin biopsy (Rosychuk & Luttgen 1995, White 1994). A biopsy of the lesion is valuable to determine if the disease is a dermatitis or if it is already a squamous cell carcinoma (Muller et al, 1985a). The aim of the study was to evaluate and describe macroscopically and histomorphologically feline facial biopsies with diagnosis of squamous cell carcinoma.

Materials and Methods

Facial biopsies from 11 cats, nine females and two males, obtained from lesion sites and with diagnosis of squamous cell carcinoma were evaluated. Biopsies were fixed in 10% buffered formalin solution. Specimens were macroscopically evaluated and routinely processed for paraffin embedding. Sections obtained were 5μm thick and were stained with the Hematoxylin and eosin technique for histopathological evaluation to confirm the diagnosis and give morphological description. The squamous cell carcinomas were classified in two different morphological types: the keratinizing squamous cell carcinoma and the non-keratinizing squamous cell carcinoma according to Mukaratirwa et al (2001). This research was in accordance with the principles of COBEA (Colégio Brasileiro de Experimentação Animal).

Results

Cats' ages varied from seven to 25 years, mean age of approximately 12 years. Among the studied facial biopsies, lesion sites were: nose, eyelid, pinna and temple. Four animals (36.4%-4/11) had lesion in the nose, three (27.3%-3/11) in the pinna and one (9.1%-1/11), in the eyelid. There were animals that had more than one lesion site. One animal (9.1%-1/11) had lesions in both the nose and temples, another (9.1%-1/11), in the nose and the eyelid. Only one animal (9.1%-1/11) had lesions in three different locations: nose, pinna and temples. Macroscopic evaluation showed that specimens size varied from 0,1cm diameter to 1.2 x 0.6 x 0.3cm. Eight (72.7%-8/11) were alopecic specimens and three (27.3%-3/11) were coated. The histopathological analysis showed that one animal (9.1%-1/11) had carcinoma in situ, one (9.1%-1/11) had nonkeratinizing squamous cell carcinoma and nine (81,8%-9/11) had keratinizing squamous cell carcinoma. All the keratinizing squamous cell carcinoma and the carcinoma in situ revealed some cells with intracellular keratin (90.9%-10/11). Keratin pearls were found in samples of six cats (54.5%-6/11) all of them from the group of keratinizing squamous cell carcinomas (66.6%-6/9). The samples of eight animals (36.4%-8/11) had thickened adjacent epidermis and the samples of one animal had thin adjacent epidermis. The whole specimen was composed of the neoplasia in two animals. In four cats (36.4%-4/11) specimens had epidermal ulceration. Hyperkeratosis was seen in the samples of five (45.5%-5/11) animals. Neoplastic cell invasion to adjacent connective tissue was seen in samples of a cat diagnosed with a keratinizing squamous cell carcinoma. Invasion to adjacent muscles was also observed in another keratinizing squamous cell carcinoma. Besides these two samples with compromised margins, samples from other seven animals with keratinizing squamous cell carcinoma were entirely compromised by neoplastic cells (81.8%-9/11). The neoplastic cells from the carcinoma in situ showed mild pleomorphism. The cells from non-keratinizing squamous cell carcinoma were moderately pleomorphic, but high mitotic rate and extensive necrosis were found. Among keratinizing squamous cell carcinoma specimens, six animals (66.7%-6/9) had neoplastic cells with moderate pleomorphism, two (22.2%-2/9) with moderate to severe pleomorphism and one (11.1%-1/9) with severe pleomorphism. Anaplastic areas were observed in the specimens of the keratinizing squamous cell carcinoma with severe pleomorphism. Samples from seven animals (63.6-7/11) showed hemorrhage. Specimens of five animals (45.5%-5/11) showed mixed inflammatory infiltrate and specimens of two cats (18.2%-2/11) revealed neutrophilic infiltrate. Lymphoplasmacytic infiltrate was seen in specimens of one animal (9.1%-1/11). A predominance of mastocytes was seen in specimens of three cats (27.3%-3/11). The main cytologic characteristics were nuclear hyperchromatism (72.7%-8/11), evident nucleolus (90.9%-10/11), but atypical mitosis were also observed (18.2%-2/11).

Discussion and Conclusions

According to Mukaratirwa et al. (2001), the keratinizing squamous cell carcinoma consists of solid cellular infiltrative masses, composed of polygonal to spindle shaped cells arranged in lobules, or cords separated by thin connective tissue and of keratin pearls in the center of some lobules. Slayter & Boosinger (1994) also describe that most cases of squamous cells carcinoma consist of islands, cords and trabeculae of invasive epithelial cells that almost always have an association the overlying epidermis, in with there has been a breaching of basal lamina zone. The present research found that 81.8% of the studied facial squamous cell carcinomas have those characteristics compatible with keratinizing squamous cell carcinoma except for fact that the keratin pearls were found only in 66.6% of the tumours from this group. According to Slayter & Boosing (1994) there is often the formation of keratin pearls (concentric lamellae of keratin within the tumor) by invasive neoplastic cells. Whereas those tumors that are well differentiated form keratin pearl, poorly differentiated tumors only show keratinization of individual cells. Mukaratirwa et al. (2001) also give a concept of the non-keratinizing form which consists of nests of cells composed of polygonal or spindle shaped cells. This research found the characteristics of nonkeratinizing squamous cell tumor in the samples of only one animal, while Mukaratirwa et al. (2001) found it in 5 of a total of 17 nasal squamous cell tumors. Withrow (1989) says that depending on the moment of the biopsy the squamous cell carcinoma can be described as carcinoma in situ superficial squamous cell carcinoma or highly infiltrating squamous cell carcinoma. Based on that our study shows that in the samples of one animal carcinoma in situ was found, and in the samples of two animals, there was infiltration of the inner tissue, characterizing highly infiltrating squamous cell carcinoma. Because the tumor is highly infiltrative (Mukaratirwa et al. 2001), margins of the specimens are usually not safe from tumor cells, as seen in this study. Specially biopsies from the face are usually small and hard to be done with a correct diameter, considering the margins. Slayter & Boosing (1994) found that there is often a desmoplastic reaction in the surrounding dermis and subcutaneous tissue in response to the invasive neoplastic squamous epithelial cells. Considering the host reaction to the neoplastic tissue, it was found inflammatory infiltrate in many specimens of the present study, that occurred because superficial perivascular dermatitis is an early stage of the UV radiation lesion (Muller et al, 1985a). In addition, numerous plasma cells may be found in the stroma. In some tumors, particularly in areas of keratinization, there is extensive infiltration by neutrophils. The cytologic features of the tumor cells are variable, depending on the degree of differentiation of the cells. In many instances, however, the cells and nuclei are large, nuclei are hyperchromatic, and chromatin after appears clumped. Nucleoli vary in size and may be prominent (Slayter & Boosing, 1994). The present research found 18.2% of atypical mitosis, nuclear hyperchromatism (72.7%), prominent nucleoli in 90.9%. The Non-keratinizing squamous cell carcinoma had a high mitotic rate and extensive necrosis, similar to the ones described before, indicating high malignancy (Mukaratirwa et al. 2001). In conclusion the keratinizing squamous cell carcinoma seems to be more common than the non-keratinizing squamous cell carcinoma in specimens from the face of the cat. Even though the non-keratinizing squamous cell tumors show many malignant features, keratinizing squamous cell carcinoma may also reveal those features, which reveals difficulty in determining the real malignancy of the tumor by that classification.

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