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Among 92 dairy goats, mainly of Saanen breeding, necropsied during studies on slow viral diseases, 17 (25.3%) of 67 over 2 years old had thymoma. Ten were females and seven were castrated males. In none was the thymoma accompanied by clinical signs attributable to it. Except for one at the thoracic inlet, all tumors were in the cranial mediastinal cavity. Encapsulated and sometimes cystic, they varied from a 2-centimeter nodule to a smoothly bosselated 10x8x8-centimeter mass weighing 300 grams. Although they were composed of lymphocytes and epithelial cells, small lymphocytes predominated in 16. One was predominantly epithelial. Hassall's corpuscles and myoid cells were seen in all tumors. In 12 tumors, small veins were encircled by spaces that varied from empty clefts to wide, fluid-filled cavities. The high prevalence of thymoma in these goats supports previous reports that this tumor occurs more often in Capra hircus than in other domestic animals. It may be one of the more common neoplasms in older goats.

The etiology of sporadic bovine leukosis (SBL) is not known. Long-term monolayer cultures were made from calf (CLS), thymic (TLS) and skin (SLS) forms, and serological tests, electron microscopic observations and reverse transcriptase assays were employed for the detection of an etiological agent. Bovine leukosis virus (BLV) antigen and reverse transcriptase activities remained negative in cultures from SBL cases. Treatment of a culture from CLS 3178 with 5'-iodo-2'-deoxyuridine and dexamethasone resulted in production of BLV which may have been acquired from the BLV-infected dam of CLS 3178, and in an alteration of cell morphology. Focus formation in monolayer cultures and colony formation in soft agar cultures were observed in this treated cell line. Human fetal lung fibroblast cells cocultivated with the cultures from SBL resulted in rapid proliferation of cells with an increased focus formation.

A retrospective study of 15 thymomas in domestic animals showed four animals had antemortem signs of dyspnea and grossly visible lumps in the thoracic inlet. The neoplasms were single, multilobulated, encapsulated masses in the anterior mediastinum or thoracic inlet. Cells with clear cytoplasm comprised the bulk of two canine thymomas, whereas the remaining neoplasms had a mixed population of ovoid and spindle-shaped cells. There were lymphocyte populations of varying density in all thymomas. Three thymomas contained structures similar to hyalinized cells and Hassall's corpuscles of normal thymus. Metastatic lesions were not seen but there were implantations on the pericardium in one cat. There was capsular invasion in the ovine thymomas.

Thymoma was diagnosed in 15 dogs at Angell Memorial Animal Hospital between 1972 and 1983. All thymomas developed in the cranial portion of the mediastinum. An autoimmune paraneoplastic syndrome was observed in 10 (67%) of the dogs and included myasthenia gravis, nonthymic neoplasms, and polymyositis. Clinical signs were variable and inconsistent, depending on whether they were attributable to the cranial mediastinal mass or to the paraneoplastic syndrome. Eleven dogs were necropsied. Two thymomas had gross characteristics of malignancy. In 3 cases, a cell consistent with a subclass of mast cell was found and in 1 thymoma, melanocytes were observed.

The features of 192 primary thymic tumours occurring in the rat are described. Of these neoplasms, 170 were classified as benign thymomas, one as a benign fibrous histiocytoma, 20 as various types of malignant thymoma, 3 lympho-epithelioma-like carcinomas, one mixed small cell undifferentiated-squamous cell carcinoma, one sarcoma-like carcinoma, 4 undifferentiated carcinomas, 11 squamous cell carcinomas and the one remaining tumour as a carcinoid. A mouse, anti-epithelial, monoclonal antibody, lu-5, was used to confirm the epithelial nature of the malignant thymomas, and neuron-specific enolase to confirm the diagnosis of carcinoid. The tumours showed many features in common with those reported in man.

A classical combination of myasthenia gravis and a thymoma is reported for the first time in a cat. The clinical symptoms, pathophysiological and histopathological characteristics are discussed.

The oncogenic capacity of a myc-containing strain of feline leukemia virus (FeLV), termed LC-FeLV, has been examined after inoculation of the virus into neonatal kittens. Like other myc-containing strains of FeLV, LC-FeLV may induce with relatively short latency, but does not necessarily induce, thymic lymphosarcoma in viremic animals. Naturally occurring and experimentally induced tumors are T-cell lymphomas which contain clonally integrated LC-FeLV proviral DNA and which cannot readily be cultivated in vitro in the presence or absence of exogenously supplied interleukin-2. Acquisition of myc by FeLV decreases the period of latency before the appearance of tumors but does not expand the spectrum of tumors induced by FeLV alone.