Cancer is a life threatening ailment and emerged as the leading cause of death in pet animals. Among pet animals, dog is the most commonly affected animal with more than 30% deaths occur due to cancer¹,². Around 50% of old age dogs develop tumourous growths and from them approximately 25% eventually dies³. Among canine tumours, cutaneous and mammary tumours accounts for maximum and it is reported that occurrence of malignant skin tumours are approximately equal to the benign skin tumour⁴. Early and accurate diagnosis of tumour cases can lead to a favourable prognosis.

Histopathology of tumour tissues reveals the exact morphology of the neoplastic cells along with their distribution and organization, thus it is considered as the gold standard for diagnosis and grading of tumours. It enables pathologists to prepare the mitotic index and stain the sections with special stains like silver nitrate method by which AgNORs can be counted and thus help in evaluating the nature of tumour⁵. But histopathology requires invasive sampling methods and few days for processing of the tissue samples. So, cytological techniques provide a good alternate to get rapid diagnosis.

Cytology provides a quick, inexpensive, less painful and easily repeatable technique for the diagnosis of suspected tumour cases. It is good technique for immediate diagnosis due to its high sensitivity and low cost⁶ and has been utilized in veterinary practice for diagnosis of different lesions in dogs. This technique is commonly used for cutaneous, mammary gland tumours and palpable lesions⁷. Besides tumour diagnosis, cytological examination can be used for the diagnosis of various other types of diseases⁸. Cytological diagnosis can vary from person to person, so it should be evaluated the sensitivity and specificity in every laboratory. Therefore, the aim of present study was to correlate the cytological and histopathological diagnosis, and to calculate the sensitivity and specificity of cytological diagnosis in the canine skin tumours.

Out of the total 66 cases, neoplasia was diagnosed in 55 by cytological method. Cytologic diagnoses included 38 epithelial tumours, 3 mesenchymal tumours and 11 round cell tumours. Epithelial tumours included 26 cases of mammary tumours, 7 hepatoid adenomas, 3 basal cell carcinomas, one each of seminoma and sertoli cell tumour. Cytologically, the mammary tumours were characterized by cluster of cells, round nucleus, moderate amount of basophilic cytoplasm, marked anisocytosis and anisokaryosis, increased nucleus to cytoplasm ratio and amorphous basophilic secretory product in cytoplasm. Similarly, perianal gland adenoma (Fig. 1,2) cases showed large hepatoid cells with small round nucleus. The basal cell carcinomas (Fig. 3,4) showed clusters of tightly adherent round, cuboidal or oval cells while seminoma had neoplastic cells with variable amounts of bluish cytoplasm and large, round nuclei and sertoli cell tumour showed large round to elongated cells with hyperchromatic nuclei and clearly visible nucleolus.

Round cell tumours included transmissible venereal tumour (6 cases), mast cell tumours (3 cases), lymphosarcoma (one case) and histiocytoma (one case). The cellularity of cytological smears of TVT (Fig. 5, 6) was high with round individual cells arranged in a sheetlike pattern, presence of distinct, clear cytoplasmic vacuoles and frequent mitotic figures. The smear of mastocytoma (Fig. 7, 8) revealed high cellularity of round, individual and uniform cells with cytoplasmic granules and variable number of eosinophils. Lymphosarcoma (Fig. 9, 10) exhibited presence of large lymphoblasts with dark hyperchromatic nuclei and bluish cytoplasm, round or irregual nuclei and frequent mitotic figures. Histiocytoma case revealed uniform population of round, oval or irregularly shaped cells with abundant cytoplasm.

Mesenchymal tumours included 2 cases of fibrosarcoma and one case of liposarcoma. Fibrosarcoma showed moderate number of large, oval cells in small clusters, marked nuclear pleomorphism and high nuclear: cytoplasm ratio. Liposarcoma revealed presence of variable shape and size adipocytes in clumps with abundant clear cytoplasm and a small condensed eccentrically placed hyperchromatic basophilic nucleus, few mitotic figures and high cellularity. Cytopathological examination of cases with ulceration revealed the presence of necrotic cell debris, inflammatory cells, including degenerated neutrophils, lymphocytes and macrophages along with neoplastic cells.

Histopathological examination revealed neoplasia in 52 cases while three cases were found to be false positive. Nine cases which were diagnosed nonneoplastic in cytology were confirmed by histopathology as true negative, however, two cases were found to be false negative. Based on this data, the sensitivity of cytological diagnosis was found to be 96.29% and the specificity 75%.

FNAB method is easy and less expensive with little or no risk to the patient and also provides the immediate diagnosis. Cytological interpretation is often valuable in establishing a diagnosis and thus, helpful in designing the appropriate therapy. Timely and appropriate therapy in the tumour cases can lead to a favourable prognosis. In the present study, among all tumours, TVT showed high cellularity, whereas moderate cellularity was found in perianal gland adenoma and basal cell carcinoma as described in the earlier studies¹¹,¹². The sensitivity and specificity of cytological diagnosis was calculated using histopathology as the standard and it was found to be 96.29% and 75%, respectively. Earlier studies showed a wide range of sensitivity and specificity of the cytological diagnosis which varied from 80 to 95% and depended upon the sample processing techniques, tumour type and expert opinions from the pathologists⁸,¹³. The results from present research showed a lower percentage of false positive and false negative diagnosis than the results of earlier authors¹⁰,¹³.

False positive results are accepted as the pathologist‘s error commonly related to lack of necessary expertize, inadvertence, or usage of staining techniques of low quality. A false positive result can be obtained because of the presence of cellular atypism caused by a reactive inflammatory process. False positive results are dangerous as they could be the cause for unnecessary surgical intervention and risky irradiation or chemotherapy. A great percentage of the false positive diagnoses and errors in cytological practices could be avoided by improvements in the techniques of obtaining samples and staining of the cytological materials. Despite the constantly expanding capabilities of cytological testing, the diagnostic value of the method has its limitations. One of the primary imperfections of cytodiagnostic puncture is the anatomo-topographical limitation of the obtained material.

In conclusion, although cytopathological examination has not yet come into extensive use in veterinary medicine for the diagnosis of tumours, the results obtained in the present study suggest that cytopathology is a practical tool for the early diagnosis of skin neoplasms. Therefore, improved cytopathological technique and interpretation can lead veterinarians to early and rapid diagnosis of the canine tumour cases, which in turn will help in designing the treatment regimen for the cases and may improve prognosis.

The authors are thankful to the Director, ICAR- Indian Veterinary Research Institute, Izatnagar, for providing the necessary facilities for carrying out the present research work. The first author is grateful to the Indian Council of Agricultural Research, New Delhi, for providing financial assistance in the form of scholarship during the course of the study.

REFERENCES