Neoplasms among canine species are twice more common in comparison to human¹, which progress more rapidly and having similar anatomical and cytochemical properties, proving them as an excellent animal model for emulating human cancers. Diagnosis of cancer, which is a prime requirement to take up treatment, is achieved in the field of oncology mainly by morphological and microscopic examinations including cytology, histopathological and immunohistochemical techniques. SCC originating from squamous epithelial cells presents varying features from incomplete carcinoma in intraepidermal form to highly malignant tumor type in its invasive form, exhibiting different degrees of differentiation in member cells of its progeny². Grossly SCC occurs as a nodular or erosive lesion presenting as red firm plaque to a cauliflower like ulcerated mass and may be seen in any organ of the body lined by epithelium like skin, eye, oral, nasal cavities, tongue, esophagus, lung, penis, vagina and footpad^3,4. Cytologically SCC exhibits striking features like anisokaryosis, anisocytosis, perinuclear halo, binucleation, multinucleation and characteristic coloration of cytoplasm with different stains⁵. Though cytological as well as histological diagnosis of well differentiated SCC is relatively an easy task, confirmation of poorly differentiated SCC requires further evaluation employing immunohistochemistry (IHC) to detect specific tumor markers⁶.

SCC a neoplasm of epithelial origin is frequently observed in the skin of dogs and represents about 5% of cutaneous tumors in this species. It can be extremely invasive and destructive with gradual loss of cutaneous tissue; however, metastases are rarely observed and occur only in late phase of the disease. The regional lymph nodes and the lungs are the most common locations for the metastasis of SCC. Regardless of tumor location, SCCs can be classified into different grades of differentiation: well differentiated, moderately differentiated and poorly differentiated⁷. Differences in clinical and histopathological features may be observed among them. The well differentiated subtype is most commonly observed in canine species, which is characterized by masses or cords of neoplastic epithelial cells that proliferate and invade the dermis and subcutis. The hallmark of this subtype is the presence of keratin pearls in varying numbers and size, which are composed by concentric layers of squamous cells with gradual increase of keratinization toward the center⁸. Currently, little is known about the clinicopathological and immunophenotypical behavioral of canine SCC. Most of the available literature is related to human SCC. However, despite having great importance of these studies in Veterinary Medicine, it has become clear that there is a need for specific knowledge that may be helpful in decisive diagnosis, prognosis and thus for therapeutics. The present communication reports a case of SCC involving right posterior mammary region in a male dog with particular emphasis on the cytological, histopathological and special staining features of the tumor.

An eleven-year-old male intact Pit Bull dog presented to Veterinary Polyclinic Lalhri Distt Una, with history of multiple cutaneous ulcerative lesions in the area of right posterior mammary gland besides progressive weight loss and reduced appetite. On clinical examination the dog revealed average body weight, normal breathing patern, heart rate of 130 beats per minute and rectal temperature of 39.7°C. The lesion had an average measured diameter of 9–10 cm presenting necrosis and surface ulcerations with hemorrhagic purulent exudate. The mass was adhered to the skin adjacent to last right mammary gland with moderately enlarged right inguinal lymph node.

Fine needle aspiration cytology and touch impression smears from the growth were prepared and stained with giemsa staining technique. Surgical resection of the lesion involving mammary tissue was made. The excised tissue grossly presented as grayish irregular lobulated subcutaneous mass. The representative tissue pieces preserved in 10% neutral buffered formalin were subjected to routine histopathological evaluation. The diagnosis of a well differentiated SCC was made on the basis of cytological findings and further confirmed on histopathological analysis and special staining with Masson’s trichrome.

Grossly growth varied in size, appeared as irregular mass with superficial necrosis and surface ulcerations (Fig. 1). The cut section of the tumor mass revealed rough surface having pink to light brown color (Fig. 2). These observations were in conformity with the earlier findings⁵. A complete blood cell count on the day of presentation revealed normal hemoglobin (Hb), hematocrit and total erythrocyte count. However, total leukocyte count (TLC) was elevated with marked neutrophilia (Table 1). Blood picture was negative for blood parasites.

Cytological smears revealed large number of malignant squamous cells occurring either individually or in clusters. The cells were pleomorphic, round to caudate in shape exhibiting prominent anisokaryosis and anisocytosis. Anisokaryosis characterized by nuclei, varying from pyknotic to large type, variable nuclear to cytoplasmic ratio, binucleation and multinucleation and perinuclear vacuolation were observed (Fig. 3). Such observations were in accordance with the previous observations^7,8. Further, asynchronous cytoplasmic (Fig. 4) and nuclear maturation, varying number of keratinized squamous cells depending upon the degree of differentiation of SCC were also observed. The cytoplasm of keratinized cells appeared bluish to purplish in Giemsa stained smears. These results were well supported with the previous findings⁷. Cytological smears also revealed a large number of polymorphonuclear and mononuclear cells. This observation was similar to earlier findings⁹ and was obvious as tumor mass was ulcerative or inflamed with suppuration in the present study.

The well differentiated SCC encountered in the present study was featured by cords or nests of proliferating neoplastic cells consisting of immature polyhedral cells at the periphery and eosinophilic highly lamellated keratin pearls at the centre (Fig. 5). The amount of keratin was abundant in well differentiated SCC type. The proliferating cells revealed moderate cellular pleomorphism, large vesicular nuclei, prominent nucleoli, variable mitotic activity and prominent intercellular bridges (Fig. 6). Similar microscopic observations have been reported¹⁰. The perinuclear halo or vacuolation observed in the present study was attributed to the presence of colorless keratohyaline granules as reported earlier⁹. The lamellated keratin in Masson’s trichrome appeared brick red (Fig. 7). This special stain also facilitated in demarcating the amount of connective tissue that varied from moderate to marked. The connective tissue was particularly abundant around invading cords in deeper areas of the neoplasm. These findings are in accordance with the previous workers ^5,10 who observed fibroplasia or desmoplasia to be abundant around penetrating epithelial cells in the deeper areas of the neoplasm. Further the focal to multifocal areas of necrosis and inflammatory infiltration with lymphocytes, plasma cells and neutrophils was in concordance with previous observations^5,7.

Squamous cell carcinoma is a relatively more common and fatal neoplasm in dogs with rapid metastasis. The present case was a well differentiated SCC with lamellated keratin pearls and marked fibroplasia or desmoplasia in the deeper area of the neoplasm. The cytological and histopathological evaluation accompanied by special staining not only favored rapid diagnosis with the degree of cellular differentiation which was also of a good prognostic value to clinicians.

The authors are thankful to the Director, Himachal Pradesh State Animal Husbandry Department and Deputy Director, Animal Health/Breeding, Distt-Una for providing necessary facilities for the present work.

References