Species hybridization is possibly the widest form of outbreeding (natural or anthropogenic) and produces interspecific hybrids with lower fitness and restricted fertility as compared to their parents. Tigon is a hybrid offspring of a tiger and a lioness¹. Tigon is rarely found in the free range wildlife. Cancers are frequently attributed as cause of death in various species of wild animals and are compared fairly well in occurrence as that of humans. Thus adversely affect the conservation efforts in some endangered species². Disease monitoring of captive animals, primarily those in zoos and aquariums, reveals a wide range of spontaneous neoplasia across the vertebrate taxa². In wild animals, neoplasms are most frequently encountered in aging captive animals and most of neoplasms of internal organs in wild animals are incidental necropsy findings³. Retrospective mortality studies in two zoos have shown similar rates of neoplasia in captive wildlife to those in domestic animals^4,5. Spontaneous neoplasms including fibrosarcomas were frequently reported in captive wild felines as well as in other carnivores^6,7,8. Fibrosarcomas are uncommon in internal sites. The most common site in the dog and cat is the skin and subcutis, and the tumors are late to metastasize^9,10. It has been reported that malignant tumors more predominant over benign especially in felids of Indian zoos⁶. It has been reported in captive felids that administration of medicines having irritant components, adjuvant related tissue reaction in vaccines and feline sarcoma virus has also found to cause neoplastic lesions¹⁰. These tumours which develop at or near vaccination sites have been called vaccine induced or postvaccinal sarcomas^11,12,13.

A 20 year old tigon, which was rescued from circus and housed at Nahargarh Rescue Centre, Jaipur, Rajasthan, showed a small growth on the ventral aspect of abdomen (Fig. 1). The growth kept on increasing in size even after treatment. A biopsy tissue was collected and based on histopathology the case was diagnosed as cutaneous fibrosarcoma. The tumour was removed surgically but the condition of the animal was continued to be deteriorating in the next two months and it died suddenly due to respiratory distress. Systematic necropsy examination was conducted and gross lesions were recorded. The representative samples were collected in 10 per cent NBF for HPE. Paraffin embedded tissues sections of 4μm were made and stained for hematoxylin and eosin (H&E)¹⁴. Similarly, the tissue sections taken on the ploy L lysine coated slides were used to demonstrate the PCNA and vimentin markers by immunohistochemistry using formerly described methods^7,15.

On postmortem examination, the carcass was emaciated with pale mucous membranes. The lungs showed multiple variable sized greyish white nodules throughout the parenchyma and a single pea-sized similar nodule was also noticed in the renal cortex. (Fig. 2 & 3). Histopathological examination of biopsy tissue from skin showed intact epidermis. But the dermis was found highly vascularized with extensive fibroblastic proliferation extending deep into the dermis without penetrating hypodermis and muscles. (Fig. 4). The fibroblasts were fusiform to spindle-shaped with hyperchromatic nuclei and were arranged unevenly in eosinophilic fibrillar collagen matrix. Numerous mitotic figures were also observed, around 6 in number in a high power field (HPF*400) (Fig 5). The Masson’s trichrome staining (MTS) also confirmed the fibroblast proliferation. The tumour growth was found positive for PCNA and vimentin markers by immunohistochemistry (Fig. 6 & 7). The lungs showed multiple foci of numerous immature fibroblasts with elongated or oval hyperchromatic nuclei disrupting the alveolar space (Fig. 8). Similarly, metastatic foci of neoplastic fibroblast was noticed in kidney cortex.

Fibrosarcoma has been reported from many wild species in India including deer, elephant, bear, leopard tiger and lion². It is an invasive type tumour of mesodermal origin with spindle shaped cells having oval or elongated nuclei. Fibrosarcomas rarely metastasize but often grow quite fast; they can be locally aggressive infiltrating muscles and fascia. The incidence being higher in adult and old animals without any breed or sex influence¹⁶. Similarly, the present case showed visceral metastases and aggressive cutaneous form. The age of the tigon in the present study was 20 years. Several studies showed that the highest prevalence of neoplasms were reported in the mean age of 20 to 25 years^4,5. Tigons are really prone to cancer and other illnesses like most hybrid animals. Several studies showed that administration of medicines having irritant components, adjuvant related tissue reaction in vaccines and feline sarcoma virus found to cause neoplastic lesions in feline species. Similarly, misplaced darts, excessive firing impact energy and the usage of powerful projectors for darting at close range can result in trauma, contusion and considerable tissue damage which led to neoplastic transformation^10,11,12. Animal abuses in circuses are common where animals are oten mistreated to perform circus tricks resulting in painful skin lesions and chronic inflammation. The present case also having the history of misplaced darts while tranquilization and administration of vaccines. The present study puts on record a case of cutaneous fibrosarcoma with visceral metastases from anaged tigon.

The authors are thankful to Director, ICAR-IVRI and Director, Nahargarh Biological Park, Jaipur Rajasthan for granting permission and extending facilities to carry out this study.

References