SQUAMOUS cell carcinoma of the sinuses has been described in many animal species, particularly in horses (Junge and others 1984, Dixon and Head 1999, Head and Dixon 1999), dogs (Rogers and others 1996) and cats (Murphy and others 1989, Mukaratirwa and others 2001). However, none has been reported in captive, wild bovids kept in zoos. Among the order Artiodactyla, one cutaneous squamous cell carcinoma has been described in a Wyoming pronghorn (Antilocapra americana americana) (Effron and others 1977). The addax (Addax nasomaculatus), of the order Artiodactyla, class Bovidae, family Antilopinae, is the most desertadapted of the antelopes, living in sandy and stony regions of the Sahara desert (Kingdon 1997). This short communication describes the gross and microscopic examination of a captive addax living in a zoo, which had squamous cell carcinoma of the frontal sinus and nasal conchae, with pulmonary and lymph node metastases. A 10-year-old, 90 kg, male addax kept in the municipal zoo of Lignano, northern Italy, showed respiratory distress, a mucous bloody nasal discharge, anorexia and cachexia. Antibiotic therapy with intramuscular enrofloxacin failed to reduce the respiratory signs, and the addax was euthanased. A few months previously, a small cutaneous nodule in the frontal region of the animal’s head had been surgically excised. At postmortem examination, the nodule had regrown; an ovoid, 5 x 4 cm area of erosion on the right side of the frontal bone surface was evident. The bone was friable; its consistency was reduced and easy to cut. The frontal sinus contained a yellowish, spongy mass in its ventral portion, which also invaded the caudal nasal conchae through the ethmoidal bone. The same type of proliferative mass was found in the orbital cavity at the emergence of the optic nerve, and appeared to be connected to the frontal sinus. Haemorrhage was detected in the brain cortex and in the maxillary sinus. The retropharyngeal lymph nodes were hyperplastic, and some whitish nodules of approximately 0·5 cm in diameter were recognised in the lung. No other organs were involved. Samples of the neoplastic mass, retropharyngeal lymph nodes, the cutaneous nodule, lung, liver and kidney were fixed for routine histopathology. Histologically, the mass showed a diffuse proliferation of neoplastic cells of epithelial origin, with a high degree of pleomorphism and squamous differentiation (Fig 1). The tumour cells had large, ovoid and hyperchromatic nuclei, with prominent multiple nucleoli, and abundant eosinophilic cytoplasm. They showed variable degrees of squamous metaplasia and keratinisation, with an appearance of ‘horn pearl’ formation. The neoplastic growth was infiltrative, with large areas of necrosis and haemorrhage. The mitotic activity was high, at three to four mitotic figures per high-power field. The retropharyngeal lymph nodes, the nodule excised from the skin and the lung (Fig 2) were affected by neoplastic proliferation characterised by the same histological features as the mass found in the sinuses. In contrast, the liver and the kidney were not involved. Immunohistochemistry was performed on selected sections of neoplastic tissue using monoclonal mouse antihuman cytokeratin antibodies (M821, 1:100; Dako). Antigen retrieval was obtained by digestion with trypsin for 30 minutes at 37°C. The EnVision Peroxidase (K4000; Dako) detection system, using 3,3′-diaminobenzidine tetrahydrochloride (D-5905; Sigma) as the chromogen, was applied. The neoplastic tissue showed strong cytoplasmic positivity to cytokeratin, thus confirming the epithelial origin of the neoplasia. On the basis of the gross, microscopic and immunohistochemical characteristics, a diagnosis of squamous cell carcinoma of the frontal sinus and nasal conchae with retropharyngeal lymph node and pulmonary metastases was made. The many types of tissue in the nasal cavity give rise to a variety of types of neoplasm. Almost all of the malignant neoplasms reported are of epithelial origin, but some neoplasms of mesenchymal origin are also reported (Madewell and others 1976). Considering the influence of the gross anatomy of the nasal and paranasal sinus cavities on the growth pattern and spread of sinonasal tumours, neoplasias in this region can grow by expansion alone or by expansion and infiltration. Tumours of the frontoconchal sinus can readily extend via the large frontomaxillary ostium into the caudal maxillary sinus, and vice versa (Head and Dixon 1999). In the present case, the tumour invasion within the sinus cavities did not allow identification of the primary site of the tumour. However, the neoplastic growth pattern indicated that the tumour had expanded both cranially and caudally, following the anatomical communications between the sinuses. Furthermore, metastases in the retropharyngeal lymph nodes, lung and skin were detected. Distant metastases have seldom been recorded with sinonasal tumours, lymph node metastases being more commonly recorded (Head and Dixon 1999). The present case contributes to the limited information available on tumour pathology in captive wild Bovidae, highFIG 2: Multiple metastatic foci of neoplastic involvement are seen in the lung. Haematoxylin and eosin. Bar=25 μm FIG 1: Histological appearance of the neoplastic mass. There is a diffuse proliferation of neoplastic cells of epithelial origin, with high grade pleomorphism, mitotic activity and squamous differentiation. Large areas of necrosis are also present. Haematoxylin and eosin. Bar=100 μm